Well, first of all Guts, despite trying to be all aloof and emotionless, with Dad any kid who comes near him. Especially kids with a lack of purpose. I'd imagine as like the co-captain of the track team he might know Yuuto (even if he's not a soccor prodigy perhaps he's still into sports??). Try out for track kid, run from your issues.

Also....Gut suffered very similar shades of childhood abuse (but with more killing and less sports) and while I might have some of that carry over, it'd def's be an Post Awakening thing to bond over, hypothetically. He gets that self isolating feel, little buddy.