happy ending junkie; stickler for happy endings
Internet slang for someone who strongly prefers or insists on happy endings in stories, often used in fan communities.
That person is a happy ending junkie, so they absolutely won't watch movies with sad endings.
As a stickler for happy endings, I couldn't stand the ending of this novel.
A blend of ハピエン (abbreviation of ハッピーエンド 'happy ending') and the slang suffix 厨 (ちゅう, 'addict' or 'zealot').