Mon

Mon was a Welsh Corgi, small and a little thick around the middle, with fur in ginger and white.

Nothing about Mon suggested anything more than an ordinary, good-natured house pet. Walks and play with young Tenko were his pleasures. He had a protective streak as well, barking at Kotaro Shimura when the man struck Tenko for slipping into his study. Tenko poured out his misery over his father's steady abuse of his hero ambitions to the dog, and Mon did what he could to console him, which is how he came to be the first victim of the boy's Quirk.

Mon lived with the Shimura family. One afternoon, while the dog and Tenko played in the yard, Kotaro hit the boy over the study. That night Mon sat beside a crying Tenko, offering comfort, and in that exact moment Decay woke up and killed him.

The sight of what was left on the ground sent Hana Shimura into screaming panic. Tenko reached for her and killed her too, and her screams brought the rest of the household running, which finished them all.

The dog surfaces twice more, both times inside Tomura's head. Facing Star and Stripe, he works out that New Order needs a living target whose sense of identity lines up with her own understanding, and he wonders whether calling Mon by name would be enough for it to take hold. Later, when Deku forces his way into Tomura's mindscape, the memory waiting there is the beating from his father and the dog who sat with him afterward.