Ajin are people who "reset" upon death, so committing suicide is actually a tactic in this show. It's not a sense of wanting to "end it all" out of depression or hopelessness.
the main character is shown as a baby briefly in the manga— it can be assumed that this would also show up at some point in the anime, although I’ve only personally read the manga at this time
While mostly cut from the anime, a character is abused and sexually assaulted by her stepfather, leading to her committing suicide. This is only ever implied in the anime.