All things considered, I can't tell who the title's referring to. If I had to guess (instead of just saying both), I'd say Shion, but given Senma's expression (having somehow internalized wavy mouths as a person trying to hold emotion back)... alfjslkadjf... Clearly the solution is to write fanfiction in an attempt to goad you into pointing out personality fallacies.
I FRIGGIN LOVE YOUR STYLE!!! it makes it look all rugged and dirty, but yet its still clean- amazing! you do textures and backgrounds so well (: and of course the expressions on the people, and their anatomy- even the shading! its all so GOOOOOOD!!!! O: