1

Sans and Papyrus were sent to the world of My Hero Academia after Frisk kills them.
They take Mineta and Sato's places in 1-A.
Undyne is also sent to the bnha world also.

The Undertale characters belong to Toby Fox and the Bnha characters are owned by Shueisha, Viz Media, Shonen Jump, Studio bones, Funimation, and Kohei Horikoshi.