Didn't know what 'Japanese' has to do with the context, so I leaving it in 'check translation'.
I do think that was Ooi who blown up due to Kuma's cuteness. But it looks like she's the one on left (from reader pov)

edit: ah, so it was the entire Japan itself that was 'blown' up due to her cuteness?

Well, 'Japanese' would have to be 日本人, 日本の, 日本な, or the like. 日本が indicates that Japan (日本) is the subject (が) of the verb phrase (here, 爆沈).

At least it wasn't from Ooi the explosion, or the one who blows Japan by Kuma's cuteness

wait did Kuma just blew WHOLE japan isles? including Okinawa?? NOT OKINAWA TOO!!!

death by moe on a grand scale

Detonation

I can see DIO exploding in my head right now scremaing NNNAAAAAANIIIIIIIII!?!?!?!