He/It

There is a contrast between her and Denji here. In this arc, Denji won because of what his companions taught him. Reze taught him how to swim, Angel suggested the chains, Beam provided intel about her (and also acted as support). And of course Aki was there trying to protect him. Reze didn't have anyone looking out for her like that. Her handlers only trained her to brute-force every obstacle and if she doesn't manage to, is expected to just die.

This is why the pool scene is important to the character development and themes btw, despite some dumb people calling it 'gooner bait'. It gets recontextualized in the end to indicate their feelings have deepened beyond physical attraction or surface level... perfection.