I still don't understand why Narukame collapsed...

He has a heart problem since he was young. It's been told from the earlier chapter.

Oops sorry, I just reread the whole story it's turn out narukami has diagnosed with asthma since he was young. I started reading this manga three years ago and stopped myself before the match with rouzan. Coz i hate to wait for the next chapter while overflows with excitement.