Hikaru ga Shinda Natsu is the closest one to to your definition but Imma bet you already read it ╮(￣▽￣)╭
Well you can try these if you want to feel unsettled. But it's not exactly what you want.
https://www.mangago.zone/read-manga/warehouse/
https://www.mangago.zone/read-manga/heartless/
Although you might like it. It's really worth it
Tomodachi game
I havent!! Thank youu ill read this!!! >w<//////
woah, i dont think ive read these too. Hzdhgfnsshgfjse so happy, thats 4 mangas to read (incl other commenters' recs) thank you thank youuuu!!!!!!
Excited to read it!! Thank youuuu!!!!
Anyone can recommend me a manga?
you can say its psychological horror, mental torment
The feeling is like this person is creepy but were forced to be together always (classmates or new sibling or wtvr)
The person likes MC but MC is suspicious of new person and do what he/she must to survive.
I dont mind if theres smut or not between them or its just new person giving mc an unsettling feeling.
Itd be fun if a ghost possessed someone mc knows and he/she is trying to get people to believe her that "its not the "true" person!" or the new person is an impostor trying to ruin mc's life from the inside and mc is trying to prevent it
Idk, im just in the mood to feel unsettled.