Initially Yuusei bolts out away from the tuck shop to keep an eye on Carly and Papyrus, tailing their trajectory as closely as he can given the state of the battlefield in case one of them falls. Carly doesn't look too well off, after all, and neither of them are gonna do well with a descent from that sort of height.

Then the Mother of Invention blasts Strange and Steven, and out of the corner of his eye Yuusei spots Steven fly into the wall of the shop separated from his gem. He changes his own path with the intent of retrieving both Steven and his gem.