No, it is not! [Not in the way that Haru thinks! Maybe Haru is used to having rationale and instinct blur, but Rei always had a clear cut divide between the two (or so he'd like to think). He can't even push himself off Haru though he can't tell if it's because Haru's grip is just that strong or that he just doesn't want to.

Either way, the fact that he is seemingly losing control of himself over his senpai in such a vulgar way is...wrong!]

My body is acting strange. [Understatement of the century, Rei.] There is something about these ears [and tail, which is now doing its best to curl around his feet] that make it difficult for me to...

[He needs to explain. He owes Haru an explanation no matter how embarrassing it is to say. Perhaps even letting him know about this would have him let go. But he doesn't want that. Rei ]

...control myself around you. [He doesn't want to elaborate with words because any sort of vocabulary that goes beyond the level of appropriateness he's used to would just make him redder. So instead, he lets instinct take over for one second to have him lick, kiss, and then nibble at Haru's neck.

Not very cat-like behavior at all, but it's what his body's doing.]