"More wood, we need it for combustion." Senku replied without much of a thought.

He tied a piece of the rope on either end of the stick and tested to see that it did in fact bend a bit like a bow. Satisfied with that, he collected a larger branch and pulled out his axe.

Despite being made of stone, it worked fine to break the wood apart, and then he set about splitting it in half so he ended up with a flat piece, but he was already breathing pretty heavily from that exertion, sweat beading on his forehead.