diff --git a/src/entities/character/api/character.ts b/src/entities/character/api/character.ts
index ef33808b..b8cf2dcc 100644
--- a/src/entities/character/api/character.ts
+++ b/src/entities/character/api/character.ts
@@ -1,9 +1,14 @@
 import axiosInstance from '@/shared/api/axios';
-import { CharacterItemsResponse } from '../model/character.type';
+import { parseDate } from '@/shared/lib/parseDate';
+import {
+  CharacterItemData,
+  CharacterItemsRawResponse,
+} from '../model/character.type';
 
-export const getCharacterCollection = () =>
-  axiosInstance
-    .get<CharacterItemsResponse>('/character/collection', {
-      useMock: true,
-    })
-    .then((res) => res.data);
+export const getCharacterCollection = (): Promise<CharacterItemData[]> =>
+  axiosInstance.get<CharacterItemsRawResponse>('/collections').then((res) =>
+    res.data.collections.map((item) => ({
+      ...item,
+      acquiredAt: parseDate(item.acquiredAt),
+    }))
+  );
diff --git a/src/entities/character/config/character.ts b/src/entities/character/config/character.ts
index d3e27ac6..932953aa 100644
--- a/src/entities/character/config/character.ts
+++ b/src/entities/character/config/character.ts
@@ -1,65 +1,46 @@
-import { CharacterType } from '@/entities/character/model/character.type';
-
-export const CHARACTER_IMAGE_SIZE: Record<
-  CharacterType,
-  {
-    big: {
-      width?: string;
-      height?: string;
-    };
-    small: {
-      width?: string;
-      height?: string;
-    };
-  }
-> = {
+export const CHARACTER_DATA = {
   '천사 모또': {
-    big: {
-      width: '15rem',
-    },
-    small: {
-      width: '12rem',
+    imageSize: {
+      big: { width: '15rem' },
+      small: { width: '12rem' },
     },
+    description: '정산의 수호천사 등장!',
   },
   '러키 모또': {
-    big: {
-      width: '12.5rem',
-    },
-    small: {
-      width: '10rem',
+    imageSize: {
+      big: { width: '12.5rem' },
+      small: { width: '10rem' },
     },
+    description: '정산 성공! 좋은 일만 가득하길~',
   },
   '딸기 또또': {
-    big: {
-      width: '12.5rem',
-    },
-    small: {
-      width: '10rem',
-      height: '10rem',
+    imageSize: {
+      big: { width: '12.5rem' },
+      small: { width: '10rem', height: '10rem' },
     },
+    description: '정산 완료! 달콤한 하루 보내~',
   },
   '잠꾸러기 또또': {
-    big: {
-      width: '12.5rem',
-    },
-    small: {
-      width: '10rem',
+    imageSize: {
+      big: { width: '12.5rem' },
+      small: { width: '10rem' },
     },
+    description: '정산 끝났어? 이제 푹 잘 수 있겠네~',
   },
   '마법사 또또': {
-    big: {
-      height: '13.72844rem',
-    },
-    small: {
-      height: '10.98275rem',
+    imageSize: {
+      big: { height: '13.72844rem' },
+      small: { height: '10.98275rem' },
     },
+    description: '정산? 아브라카다브라! 해결 완료~',
   },
-};
-
-export const CHARACTER_DESCRIPTION: Record<CharacterType, string> = {
-  '천사 모또': '정산의 수호천사 등장!',
-  '러키 모또': '정산 성공! 좋은 일만 가득하길~',
-  '딸기 또또': '정산 완료! 달콤한 하루 보내~',
-  '잠꾸러기 또또': '정산 끝났어? 이제 푹 잘 수 있겠네~',
-  '마법사 또또': '정산? 아브라카다브라! 해결 완료~',
-};
+} satisfies Record<
+  string,
+  {
+    imageSize: {
+      big: { width?: string; height?: string };
+      small: { width?: string; height?: string };
+    };
+    description: string;
+  }
+>;
diff --git a/src/entities/character/model/character.type.ts b/src/entities/character/model/character.type.ts
index 7de3abf0..739dea3e 100644
--- a/src/entities/character/model/character.type.ts
+++ b/src/entities/character/model/character.type.ts
@@ -1,9 +1,7 @@
-export type CharacterType =
-  | '천사 모또'
-  | '러키 모또'
-  | '딸기 또또'
-  | '잠꾸러기 또또'
-  | '마법사 또또';
+import { CHARACTER_DATA } from '@/entities/character/config/character';
+
+// 새 캐릭터 추가 시 CHARACTER_DATA에만 추가하면 타입이 자동으로 확장됨
+export type CharacterType = keyof typeof CHARACTER_DATA;
 
 export interface CharacterData {
   name: CharacterType;
@@ -14,10 +12,15 @@ export interface CharacterData {
 
 export interface CharacterItemData extends CharacterData {
   id: number;
-  isUnlocked: boolean;
-  unlockedAt: string | null;
+  acquiredAt: Date | null;
+}
+
+// API 원시 응답 타입 (JSON 파싱 직후, 변환 전)
+interface CharacterItemRaw extends CharacterData {
+  id: number;
+  acquiredAt: string | null;
 }
 
-export interface CharacterItemsResponse {
-  characters: CharacterItemData[];
+export interface CharacterItemsRawResponse {
+  collections: CharacterItemRaw[];
 }
diff --git a/src/entities/member/api/assignMember.ts b/src/entities/member/api/assignMember.ts
index cff5f358..445b86a3 100644
--- a/src/entities/member/api/assignMember.ts
+++ b/src/entities/member/api/assignMember.ts
@@ -1,15 +1,18 @@
 import axiosInstance from '@/shared/api/axios';
+import { parseDate } from '@/shared/lib/parseDate';
+import { MemberProfile, MemberProfileRaw } from '../model/member.type';
 
 // 참여자 선택 api (로그인한 참여자가 정산에 참여하도록 프로필 설정)
 export const assignMember = async (
   settlementCode: string,
   memberId: number
-): Promise<void> => {
-  await axiosInstance.post(
+): Promise<MemberProfile> => {
+  const response = await axiosInstance.post<MemberProfileRaw>(
     `/groups/${settlementCode}/members/assign`,
-    {
-      memberId,
-    },
-    { useMock: true }
+    { memberId }
   );
+  return {
+    ...response.data,
+    paidAt: parseDate(response.data.paidAt),
+  };
 };
diff --git a/src/entities/member/api/getProfiles.ts b/src/entities/member/api/getProfiles.ts
index 0d08bf9e..4adf22ff 100644
--- a/src/entities/member/api/getProfiles.ts
+++ b/src/entities/member/api/getProfiles.ts
@@ -1,14 +1,17 @@
 import axiosInstance from '@/shared/api/axios';
-import { MemberProfile, MemberProfileData } from '../model/member.type';
+import { parseDate } from '@/shared/lib/parseDate';
+import { MemberProfile, MemberProfileRawData } from '../model/member.type';
 
 // TODO : 기존 groupToken들을 사용하는 방식을 settlementCode를 사용하는 방식으로 변경해야 함.
 // 모임원 조회 API - 정산 참여자 프로필 조회
 export const getProfiles = async (
   settlementCode: string
 ): Promise<MemberProfile[]> => {
-  const response = await axiosInstance.get<MemberProfileData>(
-    `/groups/${settlementCode}/members`,
-    { useMock: true }
+  const response = await axiosInstance.get<MemberProfileRawData>(
+    `/groups/${settlementCode}/members`
   );
-  return response.data.members;
+  return response.data.members.map((member) => ({
+    ...member,
+    paidAt: parseDate(member.paidAt),
+  }));
 };
diff --git a/src/entities/member/model/member.type.ts b/src/entities/member/model/member.type.ts
index 88fe6c5a..ae6726c6 100644
--- a/src/entities/member/model/member.type.ts
+++ b/src/entities/member/model/member.type.ts
@@ -27,6 +27,11 @@ export interface MemberProfile {
   paidAt: Date | null;
 }
 
-export interface MemberProfileData {
-  members: MemberProfile[];
+// API 원시 응답 타입 (JSON 파싱 직후, 변환 전)
+export interface MemberProfileRaw extends Omit<MemberProfile, 'paidAt'> {
+  paidAt: string | null;
+}
+
+export interface MemberProfileRawData {
+  members: MemberProfileRaw[];
 }
diff --git a/src/features/character-management/api/useGetCharacterCollection.ts b/src/features/character-management/api/useGetCharacterCollection.ts
index d422533b..7469319b 100644
--- a/src/features/character-management/api/useGetCharacterCollection.ts
+++ b/src/features/character-management/api/useGetCharacterCollection.ts
@@ -7,9 +7,9 @@ const useGetCharacterCollection = () =>
     queryFn: getCharacterCollection,
     // 획득한 캐릭터가 가장 앞에 오도록 정렬
     select: (data) =>
-      [...data.characters].sort((a, b) => {
-        if (a.isUnlocked === b.isUnlocked) return 0;
-        return a.isUnlocked ? -1 : 1;
+      [...data].sort((a, b) => {
+        if ((a.acquiredAt !== null) === (b.acquiredAt !== null)) return 0;
+        return a.acquiredAt !== null ? -1 : 1;
       }),
   });
 
diff --git a/src/features/character-management/ui/CharacterBottomSheet/index.tsx b/src/features/character-management/ui/CharacterBottomSheet/index.tsx
index 7d451fcc..6bacadb5 100644
--- a/src/features/character-management/ui/CharacterBottomSheet/index.tsx
+++ b/src/features/character-management/ui/CharacterBottomSheet/index.tsx
@@ -3,7 +3,7 @@ import Text from '@/shared/ui/Text';
 import BottomSheet from '@/shared/ui/BottomSheet';
 import ButtonGroup from '@/shared/ui/ButtonGroup';
 import Button from '@/shared/ui/Button';
-import { CHARACTER_IMAGE_SIZE } from '@/entities/character/config/character';
+import { CHARACTER_DATA } from '@/entities/character/config/character';
 import { ROUTE } from '@/shared/config/route';
 import useGetCharacter from '@/features/character-management/api/useGetCharacter';
 import * as S from './index.styles';
@@ -33,7 +33,7 @@ function CharacterBottomSheet({ open, setOpen }: CharacterBottomSheetProps) {
             src={data.imageUrl}
             alt={data.name}
             style={{
-              ...CHARACTER_IMAGE_SIZE[data.name].small,
+              ...CHARACTER_DATA[data.name].imageSize.small,
             }}
           />
         </S.CharacterImageContainer>
diff --git a/src/features/character-management/ui/CharacterItem/index.tsx b/src/features/character-management/ui/CharacterItem/index.tsx
index c014ff11..c284a549 100644
--- a/src/features/character-management/ui/CharacterItem/index.tsx
+++ b/src/features/character-management/ui/CharacterItem/index.tsx
@@ -17,14 +17,14 @@ interface CharacterCardProps {
 }
 
 function CharacterCard({ character }: CharacterCardProps) {
-  const { imageUrl, name, unlockedAt } = character;
+  const { imageUrl, name, acquiredAt } = character;
 
   return (
     <S.CardContainer>
       <S.CharacterImage src={imageUrl} alt={name} />
       <Text variant="body2Sb">{name}</Text>
       <Text variant="caption">
-        {unlockedAt ? format(new Date(unlockedAt), 'yyyy.MM.dd') : null}
+        {acquiredAt ? format(acquiredAt, 'yyyy.MM.dd') : null}
       </Text>
     </S.CardContainer>
   );
@@ -35,7 +35,7 @@ interface CharacterItemProps {
 }
 
 function CharacterItem({ character }: CharacterItemProps) {
-  if (!character.isUnlocked) return <LockedCharacterCard />;
+  if (!character.acquiredAt) return <LockedCharacterCard />;
   return <CharacterCard character={character} />;
 }
 
diff --git a/src/features/join/api/useAssignMember.ts b/src/features/join/api/useAssignMember.ts
index a9805627..5cd34e4b 100644
--- a/src/features/join/api/useAssignMember.ts
+++ b/src/features/join/api/useAssignMember.ts
@@ -1,13 +1,30 @@
-import { useMutation, useQueryClient } from '@tanstack/react-query';
+import { useQueryClient } from '@tanstack/react-query';
 import { assignMember } from '@/entities/member/api/assignMember';
+import { MemberProfile } from '@/entities/member/model/member.type';
+import useMutationWithHandlers from '@/shared/hooks/useMutationWithHanders';
+import { showToast } from '@/shared/ui/Toast';
 
 const useAssignMember = (groupToken: string) => {
   const queryClient = useQueryClient();
-  return useMutation({
+
+  return useMutationWithHandlers<MemberProfile, Error, number>({
     mutationFn: (memberId: number) => assignMember(groupToken, memberId),
-    onSuccess: () => {
-      queryClient.removeQueries({ queryKey: ['profiles', groupToken] });
+    onSuccess: (data) => {
+      // 응답으로 받은 업데이트된 멤버 정보로 캐시를 직접 갱신 (리패치 없이 즉시 반영)
+      queryClient.setQueryData<MemberProfile[]>(
+        ['profiles', groupToken],
+        (prev) => prev?.map((member) => (member.id === data.id ? data : member))
+      );
+    },
+    // TODO: 에러 코드 확인 후 케이스별 메시지로 세분화 필요
+    errorHandlers: {
+      default: () =>
+        showToast({
+          type: 'error',
+          content: '참여자 선택에 실패했어요. 다시 시도해 주세요.',
+        }),
     },
+    ignoreBoundaryErrors: [400, 409],
   });
 };
 
diff --git a/src/mocks/handlers/character.ts b/src/mocks/handlers/character.ts
index eb382e4f..23dcc1d3 100644
--- a/src/mocks/handlers/character.ts
+++ b/src/mocks/handlers/character.ts
@@ -1,45 +1,42 @@
 import { http, HttpResponse, passthrough } from 'msw';
-import { CharacterItemsResponse } from '@/entities/character/model/character.type';
+import { CharacterItemsRawResponse } from '@/entities/character/model/character.type';
 import getIsMocked from '@/mocks/lib/getIsMocked';
 
 const characterHandlers = [
-  http.get('/api/v1/character/collection', async ({ request }) => {
+  http.get('/api/v1/collections', async ({ request }) => {
     if (!getIsMocked(request)) return passthrough();
 
-    const dummyCharacterCollectionResponse: CharacterItemsResponse = {
-      characters: [
+    const dummyCharacterCollectionResponse: CharacterItemsRawResponse = {
+      collections: [
         {
           id: 1,
           name: '마법사 또또',
-          isUnlocked: true,
           imageUrl:
             'https://ylsrfiwjufyciwoidcaz.supabase.co/storage/v1/object/public/moddo/wizard_ddoddo.png',
           imageBigUrl:
             'https://ylsrfiwjufyciwoidcaz.supabase.co/storage/v1/object/public/moddo/wizard_ddoddo.png',
           rarity: 3,
-          unlockedAt: '2025-02-03T00:00:00Z',
+          acquiredAt: '2025-02-03T00:00:00Z',
         },
         {
           id: 2,
           name: '천사 모또',
-          isUnlocked: true,
           imageUrl:
             'https://ylsrfiwjufyciwoidcaz.supabase.co/storage/v1/object/public/moddo/angel_moddo.png',
           imageBigUrl:
             'https://ylsrfiwjufyciwoidcaz.supabase.co/storage/v1/object/public/moddo/angel_moddo.png',
           rarity: 2,
-          unlockedAt: '2025-02-03T00:00:00Z',
+          acquiredAt: '2025-02-03T00:00:00Z',
         },
         {
           id: 3,
           name: '딸기 또또',
-          isUnlocked: false,
           imageUrl:
             'https://ylsrfiwjufyciwoidcaz.supabase.co/storage/v1/object/public/moddo/strawberry_ddoddo.png',
           imageBigUrl:
             'https://ylsrfiwjufyciwoidcaz.supabase.co/storage/v1/object/public/moddo/strawberry_ddoddo.png',
           rarity: 1,
-          unlockedAt: null,
+          acquiredAt: null,
         },
       ],
     };
diff --git a/src/pages/characterShare/CharacterSharePage.tsx b/src/pages/characterShare/CharacterSharePage.tsx
index 4b4f8e5f..db32a31a 100644
--- a/src/pages/characterShare/CharacterSharePage.tsx
+++ b/src/pages/characterShare/CharacterSharePage.tsx
@@ -9,10 +9,7 @@ import { ArrowLeft, Download } from '@/shared/assets/svgs/icon';
 import Header from '@/shared/ui/Header';
 import Text from '@/shared/ui/Text';
 import { BottomButtonContainer } from '@/shared/styles/bottomButton.styles';
-import {
-  CHARACTER_DESCRIPTION,
-  CHARACTER_IMAGE_SIZE,
-} from '@/entities/character/config/character';
+import { CHARACTER_DATA } from '@/entities/character/config/character';
 import StarChip from '@/features/character-management/ui/StarChip';
 import useGetCharacter from '@/features/character-management/api/useGetCharacter';
 import * as S from './CharacterSharePage.styles';
@@ -101,7 +98,7 @@ function CharacterSharePage() {
                 src={data.imageBigUrl}
                 alt={data.name}
                 style={{
-                  ...CHARACTER_IMAGE_SIZE[data.name].big,
+                  ...CHARACTER_DATA[data.name].imageSize.big,
                 }}
               />
             </S.CharacterImageContainer>
@@ -109,7 +106,7 @@ function CharacterSharePage() {
               {data.name}
             </Text>
             <Text variant="body1R" color="semantic.text.subtle">
-              {CHARACTER_DESCRIPTION[data.name]}
+              {CHARACTER_DATA[data.name].description}
             </Text>
           </S.CharacterCard>
         </S.CharacterCardContainer>
diff --git a/src/shared/lib/parseDate.ts b/src/shared/lib/parseDate.ts
new file mode 100644
index 00000000..295c769b
--- /dev/null
+++ b/src/shared/lib/parseDate.ts
@@ -0,0 +1,13 @@
+import { isValid, parseISO } from 'date-fns';
+
+/**
+ * API 응답의 ISO 날짜 문자열을 Date 객체로 변환합니다.
+ *
+ * new Date("invalid")는 truthy한 Invalid Date를 반환해 이후 format() 등에서 RangeError를 반환하기 때문에 parseISO + isValid로 유효성을 검사한 후 변환합니다.
+ * 유효하지 않으면 null을 반환합니다.
+ */
+export const parseDate = (value: string | null): Date | null => {
+  if (!value) return null;
+  const parsed = parseISO(value);
+  return isValid(parsed) ? parsed : null;
+};