Chapter 121

Theory of Happiness is the 121st Chapter of the Chainsaw Man manga.

Summary
Yoshida takes Asa to the Devil Hunter's Club council room for some coffee, with the former saying it's ok to do so since they're both technically members. Asa wonders why he's spending time on her since he must be busy as a public devil hunter, assuming it must be because he has feelings for her. When asked about why she was mumbling at the school gates, she states she was thinking about how it’s better to live a life of solitude. Yoshida, confused about why she still said it aloud, agrees, saying that in the current day and age, single people can be as successful as someone in a relationship. Asa takes this as a sign of him liking her, and just as it seems like he was going to confess, he instead states that he wants her to stay as far away from Denji as possible. When Asa asks him why, he refuses to elaborate, before leaving.

Back in Denji and Nayuta's home, the latter picks up the most putrid scent of a devil she's ever smelt. She tries to get a lethargic Denji to get up and fight, but he says he doesn't want to fight anymore; even if all the ladies want him, what's the point of doing so if it means he’ll be denied a relationship with any of them? Seeing where she went wrong, Nayuta reasons that as Chainsaw Man, Denji could theoretically have love from the masses; something far greater than just a single girlfriend. Thinking it over, Denji agrees, now reinvigorated to fight.

Feeling dejected for being seemingly turned down a second time, a depressed Asa walks home, frustrated about her current situation. Yoru agrees with her that a life of loneliness might be better than constant heartbreak, but as soon as Asa starts thinking about how she has no redeeming qualities and that she’s arrogant for craving love, the war devil tries to comfort her, saying she's a bit too harsh on herself. Asa then remarks how she’s tired of being unable to maintain a healthy relationship, much to Yoru's stunned silence, with her even saying that she’s better off dead.

Approaching her apartment complex, Asa notices the corpse of a middle-aged man on the ground near her. Yoru quickly takes over, demanding Asa stays back, as she looks up to see every occupant of the complex outside their doors, staring directly down at them.

Characters

 * Asa Mitaka
 * Hirofumi Yoshida
 * Nayuta
 * Denji
 * Meowy
 * Yoru

Trivia
It's possible Asa's suicial thoughts were actually caused by the power of the nerby Primal Fear.