suicide boy
Tonari no Metaller-san
https://www.mangago.me/read-manga/tsuiraku_jk_to_haijin_kyoushi/ i don't know if she is emo but she is gloomy and wants to die....
(Warning: some contain dark themes/images)
Isekai Shikkaku
Mononobe Koshoten Kaikitan
Mirukarani Ayashii Futari
(these next ones are manhwa, but I think they fit your qualifications)
Nowhere Boy
Bastard (hwang Youngchan)
The Boxer
Winter Woods
Day one of asking if any of yall can recommend a good manga with like an emo and gloomy mc or ml <3