If his eyes are co-dominant or nearly co-dominant, it could be difficult to focus on the sight picture without squinting, closing, covering, or otherwise limiting the sensory input from one eye. The reason many people insist that everyone should train to shoot with both eyes open, regardless of the quirks of their individual bodies is because they assume that it is better or more instinctive to keep both eyes open and on the “threat.” However, the only thing threatening Rain is a somewhat mean joke. All that being said, the character appears to be strongly right eye dominant rather than having co-dominant eyes, as the left hand is being brought all the way over to the right side. The only way this could really make much sense is if he’s actually missing an eye, (rather than it just being that the artist couldn’t draw matching eyes on a 3/4 view.)
There really are no redeeming qualities about the teacup grip. I’ve seen some claims about it adding some support with the off hand without being too different from a one-handed grip, but I can’t bring myself to actually use this argument.
I would point out that there’s other reasons to use a blading stance besides being restricted in space, but I don’t think he was trying to protect or obscure his holstered firearm from the meme or present a smaller target to the meme, and I’m fairly certain the weakness of the teacup grip undoes any benefits to the push-pull method of recoil control that might be offered by a blading stance.