two batshit insane yanderes (both suicidally depressed) in love with each other, and their love fixing their depression
also making white chocolate molds out of their love interest's teeth so they can eat fake teeth i guess
Hajime is the one that is suicidal (kind of), well expect he isn't anymore by the looks of it in this chapter. Hajime more so had a death wish according to the author's fanbox. He was wondering if he would have any regrets on the brink of death.
Yuka isn't really suicidal, she's more so self destructive and selfless, caring more about other's than her own well being, and then later changed to just caring about Hajime rather than others.
Also the reason why she made chocolate molds was because there is a finite amount of Hajime baby teeth, and so she can't eat the actual teeth because it's limited in amount. This was in the fanbox too. Basically she would have eaten his actual teeth if there was a unlimited amount.