Small children typically weren't heavy, certainly, for most people, but Senku was not most people. She weighed more than a small bundle of wood, and so she could expect a reaction until he drank the potion.

He grunted, but didn't complain as she got on his back and looped his arms under her knees, settling her in place. He groaned a little bit as he straightened up, the bag in one hand and the potion in another.

"Ready?" Senku asked, already breathing a little heavier than usual. He was fine, his body was just very uncooperative.