diff --git a/back/src/main/java/com/back/domain/scenario/repository/ScenarioRepository.java b/back/src/main/java/com/back/domain/scenario/repository/ScenarioRepository.java
index a3b8420..b7dee5b 100644
--- a/back/src/main/java/com/back/domain/scenario/repository/ScenarioRepository.java
+++ b/back/src/main/java/com/back/domain/scenario/repository/ScenarioRepository.java
@@ -82,4 +82,17 @@ Page<Scenario> findByUserIdAndDecisionLineIsNotNullAndStatusOrderByCreatedDateDe
 
     @Query("select s.id from Scenario s where s.baseLine.id = :baseLineId")
     List<Long> findIdsByBaseLine_Id(@Param("baseLineId") Long baseLineId);
+
+    @Modifying(clearAutomatically = true)
+    @Query("""
+    UPDATE Scenario s
+       SET s.representative = 
+           CASE WHEN s.id = :scenarioId THEN true ELSE false END
+     WHERE s.user.id = :userId
+       AND (s.representative = true OR s.id = :scenarioId)
+    """)
+    void updateRepresentativeStatus(
+            @Param("userId") Long userId,
+            @Param("scenarioId") Long scenarioId
+    );
 }
\ No newline at end of file
diff --git a/back/src/main/java/com/back/domain/user/controller/UserInfoController.java b/back/src/main/java/com/back/domain/user/controller/UserInfoController.java
index a6be34c..eb63cfe 100644
--- a/back/src/main/java/com/back/domain/user/controller/UserInfoController.java
+++ b/back/src/main/java/com/back/domain/user/controller/UserInfoController.java
@@ -38,14 +38,14 @@ public ResponseEntity<UserInfoResponse> getMyInfo(@AuthenticationPrincipal Custo
     @PostMapping("/users-info")
     public ResponseEntity<UserInfoResponse> createMyInfo(@AuthenticationPrincipal CustomUserDetails principal,
                                                          @Valid @RequestBody UserInfoRequest req) {
-        return ResponseEntity.ok(userInfoService.createMyInfo(principal.getId(), req));
+        return ResponseEntity.ok(userInfoService.saveOrUpdateMyInfo(principal.getId(), req));
     }
 
     // 사용자 정보 수정
     @PutMapping("/users-info")
     public ResponseEntity<UserInfoResponse> updateMyInfo(@AuthenticationPrincipal CustomUserDetails principal,
                                                          @Valid @RequestBody UserInfoRequest req) {
-        return ResponseEntity.ok(userInfoService.updateMyInfo(principal.getId(), req));
+        return ResponseEntity.ok(userInfoService.saveOrUpdateMyInfo(principal.getId(), req));
     }
 
     // 내가 만든 시나리오 목록 조회 (평행우주 목록)
diff --git a/back/src/main/java/com/back/domain/user/service/GuestService.java b/back/src/main/java/com/back/domain/user/service/GuestService.java
index 59cf79d..0084ede 100644
--- a/back/src/main/java/com/back/domain/user/service/GuestService.java
+++ b/back/src/main/java/com/back/domain/user/service/GuestService.java
@@ -27,7 +27,7 @@ public User createAndSaveGuest(){
         User guest = User.builder()
                 .email(guestEmail)
                 .username(guestLoginId)
-                .password(null) // 게스트 비밀번호 없음(추후 전환 시 설정)
+                .password(null)
                 .nickname("게스트_" + UUID.randomUUID().toString().substring(0, 4))
                 .birthdayAt(LocalDateTime.now())
                 .role(Role.GUEST)
diff --git a/back/src/main/java/com/back/domain/user/service/UserInfoService.java b/back/src/main/java/com/back/domain/user/service/UserInfoService.java
index 8169352..6c2386e 100644
--- a/back/src/main/java/com/back/domain/user/service/UserInfoService.java
+++ b/back/src/main/java/com/back/domain/user/service/UserInfoService.java
@@ -42,17 +42,7 @@ public UserInfoResponse getMyInfo(Long userId) {
     }
 
     @Transactional
-    public UserInfoResponse createMyInfo(Long userId, UserInfoRequest req) {
-        User user = userRepository.findById(userId)
-                .orElseThrow(() -> new EntityNotFoundException("User not found: " + userId));
-
-        applyPatch(user, req);
-
-        return UserInfoResponse.from(user);
-    }
-
-    @Transactional
-    public UserInfoResponse updateMyInfo(Long userId, UserInfoRequest req) {
+    public UserInfoResponse saveOrUpdateMyInfo(Long userId, UserInfoRequest req) {
         User user = userRepository.findById(userId)
                 .orElseThrow(() -> new EntityNotFoundException("User not found: " + userId));
 
@@ -85,11 +75,12 @@ public PageResponse<UserScenarioListResponse> getMyScenarios(Long userId, Pageab
         // 시나리오 id 목록 추출
         List<Long> scenarioIds = scenarioPage.getContent().stream()
                 .map(Scenario::getId)
-                .collect(Collectors.toList());
+                .toList();
 
         // SceneType 조회, 시나리오 id별로 그룹화
-        List<SceneType> sceneTypes = sceneTypeRepository.findByScenarioIdIn(scenarioIds);
-        Map<Long, List<SceneType>> sceneTypeMap = sceneTypes.stream()
+        Map<Long, List<SceneType>> sceneTypeMap = scenarioIds.isEmpty()
+                ? Map.of()
+                : sceneTypeRepository.findByScenarioIdIn(scenarioIds).stream()
                 .collect(Collectors.groupingBy(st -> st.getScenario().getId()));
 
         Page<UserScenarioListResponse> responsePage = scenarioPage.map(scenario ->
@@ -134,12 +125,7 @@ public void setProfileScenario(Long userId, Long scenarioId) {
             throw new IllegalArgumentException("Scenario does not belong to user");
         }
 
-        // 기존 대표 시나리오를 false로 변경
-        scenarioRepository.findByUserIdAndRepresentativeTrue(userId)
-                .ifPresent(existingRepresentative -> existingRepresentative.setRepresentative(false));
-
-        // 새로운 시나리오를 대표로 설정
-        scenario.setRepresentative(true);
+        scenarioRepository.updateRepresentativeStatus(userId, scenarioId);
     }
 
     public UserProfileResponse getMyProfile(Long userId) {
@@ -157,11 +143,11 @@ public UserProfileResponse getMyProfile(Long userId) {
     }
 
     private void applyPatch(User user, UserInfoRequest req) {
-        if (req.username() != null)      user.setUsername(req.username());
+        if (req.username() != null)      user.setUsername(req.username().trim());
         if (req.birthdayAt() != null)    user.setBirthdayAt(req.birthdayAt());
         if (req.gender() != null)        user.setGender(req.gender());
         if (req.mbti() != null)          user.setMbti(req.mbti());
-        if (req.beliefs() != null)       user.setBeliefs(req.beliefs());
+        if (req.beliefs() != null)       user.setBeliefs(req.beliefs().trim());
         if (req.lifeSatis() != null)     user.setLifeSatis(req.lifeSatis());
         if (req.relationship() != null)  user.setRelationship(req.relationship());
         if (req.workLifeBal() != null)   user.setWorkLifeBal(req.workLifeBal());