洪 式 極 上 撃
is what appears on the screen and he follows along saying them as he does it.
極上 Means "the best" roughly and 撃 means "strike"
Interpretting the first two means less to me, 洪 is a flood, but can also mean "vast". As for 式 the only reading I can get any sense of is "style"
So my guess at this is he's either talking about how great his attack is or naming it (if there is indeed such a arrogantly named attack). I'd defer to someone with some real east asian language knowledge though.
/edit/ or you could just listen to what the english voice actor says since thats an interpretation of them too