Yasu Matsuhita is the Ultimate Engineer. They go with the flow and seems to be always relaxed and calm. With them, Yasu has a pet rabbit (which is a dwarf hotot), named Mochi, who goes inside their toolbox whenever he's not out.

They are laid-back but still have a sense of humor. Yasu calls everybody around them kid, even if the person is older than them. Also, they fall asleep all the time, which can sometimes get them into bad situations.

There is something underneath the surface. Yasu has many things that cannot be explained away, like scars over their body...