diff --git a/src/main/java/org/websoso/WSSServer/application/LibraryInterestApplication.java b/src/main/java/org/websoso/WSSServer/application/LibraryInterestApplication.java
index d2e14d3c..decacb81 100644
--- a/src/main/java/org/websoso/WSSServer/application/LibraryInterestApplication.java
+++ b/src/main/java/org/websoso/WSSServer/application/LibraryInterestApplication.java
@@ -1,11 +1,8 @@
 package org.websoso.WSSServer.application;
 
-import static org.websoso.WSSServer.exception.error.CustomUserNovelError.ALREADY_INTERESTED;
 import static org.websoso.WSSServer.exception.error.CustomUserNovelError.NOT_INTERESTED;
-import static org.websoso.WSSServer.exception.error.CustomUserNovelError.USER_NOVEL_ALREADY_EXISTS;
 
 import lombok.RequiredArgsConstructor;
-import org.springframework.dao.DataIntegrityViolationException;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 import org.websoso.WSSServer.user.domain.User;
@@ -32,21 +29,7 @@ public class LibraryInterestApplication {
     public void registerAsInterest(User user, Long novelId) {
         Novel novel = novelService.getNovelOrException(novelId);
 
-        UserNovel userNovel = user == null ? null : libraryService.getLibraryOrNull(user, novel);
-
-        if (userNovel != null && userNovel.getIsInterest()) {
-            throw new CustomUserNovelException(ALREADY_INTERESTED, "already registered as interested");
-        }
-
-        if (userNovel == null) {
-            try {
-                userNovel = createUserNovelByInterest(user, novel);
-            } catch (DataIntegrityViolationException e) {
-                userNovel = libraryService.getLibraryOrException(user, novelId);
-            }
-        }
-
-        userNovel.setIsInterest(true);
+        libraryService.registerInterest(user, novel);
     }
 
     /**
@@ -57,25 +40,13 @@ public void registerAsInterest(User user, Long novelId) {
      */
     @Transactional
     public void unregisterAsInterest(User user, Long novelId) {
-        UserNovel userNovel = libraryService.getLibraryOrException(user, novelId);
+        UserNovel library = libraryService.getLibraryOrNull(user, novelId);
 
-        if (!userNovel.getIsInterest()) {
-            throw new CustomUserNovelException(NOT_INTERESTED, "not registered as interest");
-        }
-
-        userNovel.setIsInterest(false);
-
-        if (userNovel.getStatus() == null) {
-            libraryService.delete(userNovel);
+        if (library == null) {
+            return;
         }
 
+        libraryService.unregisterInterest(library);
     }
 
-    private UserNovel createUserNovelByInterest(User user, Novel novel) {
-        if (libraryService.getLibraryOrNull(user, novel) != null) {
-            throw new CustomUserNovelException(USER_NOVEL_ALREADY_EXISTS, "this novel is already registered");
-        }
-
-        return libraryService.createLibrary(null, 0.0f, null, null, user, novel);
-    }
 }
diff --git a/src/main/java/org/websoso/WSSServer/library/domain/UserNovel.java b/src/main/java/org/websoso/WSSServer/library/domain/UserNovel.java
index fca72eb2..66f340d4 100644
--- a/src/main/java/org/websoso/WSSServer/library/domain/UserNovel.java
+++ b/src/main/java/org/websoso/WSSServer/library/domain/UserNovel.java
@@ -36,6 +36,9 @@
 })
 public class UserNovel extends BaseEntity {
 
+    public static final Float DEFAULT_RATING = 0.0f;
+    public static final ReadStatus DEFAULT_STATUS = null;
+
     @Id
     @GeneratedValue(strategy = IDENTITY)
     @Column(nullable = false)
@@ -87,8 +90,23 @@ public static UserNovel create(ReadStatus status, Float userNovelRating, LocalDa
         return new UserNovel(status, userNovelRating, startDate, endDate, user, novel);
     }
 
-    public void setIsInterest(Boolean isInterest) {
-        this.isInterest = isInterest;
+    /**
+     * 관심 상태 지정
+     */
+    public void markAsInterested() {
+        this.isInterest = true;
+    }
+
+    /**
+     * 관심 상태 해제
+     */
+    public void unmarkAsInterested() {
+        this.isInterest = false;
+    }
+
+    public boolean isSafeToDelete() {
+        return !this.isInterest
+                && this.status == null;
     }
 
     public void updateUserNovel(Float userNovelRating, ReadStatus status, LocalDate startDate, LocalDate endDate) {
diff --git a/src/main/java/org/websoso/WSSServer/library/repository/UserNovelRepository.java b/src/main/java/org/websoso/WSSServer/library/repository/UserNovelRepository.java
index 1e367ec2..48ff0970 100644
--- a/src/main/java/org/websoso/WSSServer/library/repository/UserNovelRepository.java
+++ b/src/main/java/org/websoso/WSSServer/library/repository/UserNovelRepository.java
@@ -1,8 +1,10 @@
 package org.websoso.WSSServer.library.repository;
 
+import io.lettuce.core.dynamic.annotation.Param;
 import java.util.List;
 import java.util.Optional;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.stereotype.Repository;
 import org.websoso.WSSServer.novel.domain.Novel;
@@ -29,4 +31,28 @@ public interface UserNovelRepository extends JpaRepository<UserNovel, Long>, Use
     List<UserNovel> findUserNovelByUser(User user);
 
     Optional<UserNovel> findByNovel_NovelIdAndUser(Long novelId, User user);
+
+    @Modifying(clearAutomatically = true)
+    @Query(value = """
+        INSERT INTO user_novel (
+            user_id, novel_id, is_interest, 
+            user_novel_rating, status, 
+            created_date, modified_date
+        ) VALUES (
+            :userId, :novelId, true, 
+            :defaultRating, 
+            :#{#defaultStatus?.name()},
+            NOW(), NOW()
+        )
+        ON DUPLICATE KEY UPDATE
+            is_interest = true,
+            modified_date = NOW()
+        """, nativeQuery = true)
+    void upsertInterest(
+            @Param("userId") Long userId,
+            @Param("novelId") Long novelId,
+            @Param("defaultRating") Float defaultRating,
+            @Param("defaultStatus") ReadStatus defaultStatus
+    );
+
 }
diff --git a/src/main/java/org/websoso/WSSServer/library/service/LibraryService.java b/src/main/java/org/websoso/WSSServer/library/service/LibraryService.java
index aebeb9f0..784c48c4 100644
--- a/src/main/java/org/websoso/WSSServer/library/service/LibraryService.java
+++ b/src/main/java/org/websoso/WSSServer/library/service/LibraryService.java
@@ -44,6 +44,15 @@ public UserNovel getLibraryOrNull(User user, Novel novel) {
         return userNovelRepository.findByNovel_NovelIdAndUser(novel.getNovelId(), user).orElse(null);
     }
 
+    @Transactional(readOnly = true)
+    public UserNovel getLibraryOrNull(User user, long novelId) {
+        if (user == null) {
+            return null;
+        }
+
+        return userNovelRepository.findByNovel_NovelIdAndUser(novelId, user).orElse(null);
+    }
+
     @Transactional
     public UserNovel createLibrary(ReadStatus status, Float userNovelRating, LocalDate startDate, LocalDate endDate,
                                    User user, Novel novel) {
@@ -56,6 +65,43 @@ public UserNovel createLibrary(ReadStatus status, Float userNovelRating, LocalDa
                 novel));
     }
 
+    /**
+     * <p>관심있어요를 등록한다.</p>
+     * 서재 내역이 없다면, 서재 내역을 생성하면서 등록한다.
+     *
+     * @param user  사용자 Entity
+     * @param novel 서재 Entity
+     */
+    @Transactional
+    public void registerInterest(User user, Novel novel) {
+        userNovelRepository.upsertInterest(
+                user.getUserId(),
+                novel.getNovelId(),
+                UserNovel.DEFAULT_RATING,
+                UserNovel.DEFAULT_STATUS
+        );
+    }
+
+    /**
+     * <p>관심있어요를 해제한다.</p>
+     * 만약, 서재 정보가 없다면 삭제한다.
+     *
+     * @param library 서재 Entity
+     */
+    @Transactional
+    public void unregisterInterest(UserNovel library) {
+        if (Boolean.FALSE.equals(library.getIsInterest())) {
+            return;
+        }
+
+        library.unmarkAsInterested();
+
+        if (library.isSafeToDelete()) {
+            userNovelRepository.delete(library);
+        }
+    }
+
+    @Transactional
     public void delete(UserNovel library) {
         userNovelRepository.delete(library);
     }
diff --git a/src/main/java/org/websoso/WSSServer/novel/service/GenreServiceImpl.java b/src/main/java/org/websoso/WSSServer/novel/service/GenreServiceImpl.java
index a5b0bb24..69e3272a 100644
--- a/src/main/java/org/websoso/WSSServer/novel/service/GenreServiceImpl.java
+++ b/src/main/java/org/websoso/WSSServer/novel/service/GenreServiceImpl.java
@@ -32,7 +32,7 @@ public List<Genre> getGenresOrException(List<String> names) {
 
         List<String> uniqueNames = names.stream().distinct().toList();
 
-        List<Genre> genres = genreRepository.findByNameIn(uniqueNames);
+        List<Genre> genres = genreRepository.findByGenreNameIn(uniqueNames);
 
         if (genres.size() != uniqueNames.size()) {
             throw new CustomGenreException(GENRE_NOT_FOUND,
diff --git a/src/main/java/org/websoso/WSSServer/repository/GenreRepository.java b/src/main/java/org/websoso/WSSServer/repository/GenreRepository.java
index 6facddcc..b06e6724 100644
--- a/src/main/java/org/websoso/WSSServer/repository/GenreRepository.java
+++ b/src/main/java/org/websoso/WSSServer/repository/GenreRepository.java
@@ -11,5 +11,5 @@ public interface GenreRepository extends JpaRepository<Genre, Byte> {
 
     Optional<Genre> findByGenreName(String name);
 
-    List<Genre> findByNameIn(List<String> names);
+    List<Genre> findByGenreNameIn(List<String> genreNames);
 }