Even though he was hit by a severe wound, Rio was already quite immune to pain, and he was incapable of feeling fear and intimidation, so he wasn't afraid either.
But Rio was definitely surprised by how amazingly Raika had copied all the skills of the people that Rio knew.
'He's able to know everything about me for some reason… but how…'
Rio then remembered that Raika didn't seem to know about the existence of 'True Immunity,' and he was also surprised when Rio nullified his control over miasma so easily.
'He's not able to know everything if I look at it this way… but what makes him unable to know about 'True Immunity,' though?...'
'Is it because this skill is not something anyone can sense or predict?'
Ever since Rio first got 'True Immunity,' he's been surprised by its ability to deal with many dangerous situations easily!
