Aside from the fact that they actually need to meet face to face at some point (and compare names, so Dun can be amused by Starsong and Kengo can potentially recognize Dun's), I've been tossing around the idea of Kengo trying to learn martial arts from him. Kengo seems to pick up on it pretty easily in canon (about twelve episodes ahead of where I took him from) and even though he has his health issues, it would help him feel a bit more useful.

I think Kengo's already staked a claim on Dun looking out for him, at least a little.