Guys, he was a Japanese man who never killed anyone before in his life, & this time he just literally blew up because two psychos decided to be opportunistic genocidal megalomaniacs. It can't be helped that he tried to find normalcy in the next country he stumbled into, while being assisted by two empathetic mythical animals that can see his unblemished soul behind that curse... rather than he'd become an unstable, PTSD-triggered dangerous loose cannon. As the protagonist, he has always been a foolishly positive, loyal & overworking persevering good dude since his past life. That's his redeeming traits he should always keep or he'd become a bipolar fugitive instead.
But I can bet if he'd find a second family to protect, he'd unleash his hidden demons again to the unlucky enemies. You wouldn't always know that the most cheerful positive good dude often hides their demons deep inside their soul, because there's simply no need to show it to strangers.