Welp, guess that confirms my fears. You know, this reminds me of UchiMusume. Lots of people claim what happens in that story is “grooming”, implying the MC cultivated Latina into his wife. I think that is better applied here with Reiji, or at least close enough. He uses his position as Rin’s guardian to eventually have that sort of relationship and get close enough right now so that it isn’t considered sexual but still has undertones. I wouldn’t call it grooming YET because he hasn’t abused his position as a guardian, but it seems he is planning to down the line so he is plotting to groom Rin.
All this to say, fuck Reiji. This is an actual groomer or a would-be one. Just further cements my position on stories like UchuMusume and Usagi Drop not being stories involving grooming.