Thing is, his masters are blatantly superhuman. They have feats like running on water, toppling tanks, moving so fast they create multiple after images, smashing huge rocks like nothing, knocking out a crowd of professional fighters with just their auras, etc.
If Kenichi was at those levels, Batman would be shredded to bits unless he has tools and prep.
Kenichi raaaaaaapes.
The best of them is the Invincible Superman, and even when a slow kick from him was slowed down by like 1/1600, it was still barely a blur. Kenichi takes hits from him and fights with him(he's obviously holding back) but does incredibly well.
Even if Batman could hit him, his training has made him so durable that it wouldn't do anything. And each of Kenichi's hits would set Batman's life straight. If the first one didn't ko him and break every bone in his body.