Honestly, I still can’t tell how old Masashi is supposed to be. On the one hand, he is usually always described as a child, is rather meek/short in physical height, and acts childish, so could be around 14ish. On the other hand, I have a really hard time imagining a 12-14 year old having as a mature intellectual outlook as Masa seems to. So based on that, and his/her magical skill, and dialog in books 1 and 2, I had thought he was at least 16ish–the MC describes him as around the same age as the young women in book 2 who were crushing over the Kabuki actor in the theater. So around the same age, as Ige, I thought, at least? Who is a teenager.
Of course an MC over the age of 20 or 30 would probably still think of a 16-18 year old as a “kid” in any case. It’s unclear how old the MC actually is, but we can say they definitely “feel” old, due to the hard life they have led, and aging isn’t seen as a good thing for a warrior/samurai. And if the MC is female? In a society like that, you’d be considered over the hill if you didn’t marry young, I imagine. I know, historically, it wasn’t that unusual for people to marry (and die) young. Life expectancy being what it was.
Still, I don’t see the MC as having any perverted intentions towards Masa at all (even if they do joke/tease sometimes) as Jun claims. Masa might have a crush on the MC, but the MC seems to instead value being close to someone in a non sexual way for once, as we can see with their friendship with Hatch.
It’s also apparent that some part of the MC is emotionally stunted too as a child due to his/her traumatic past, as reflected in how they appear to Masa as a child in the dream sequence at the end of book 1. There are at least two places where the MC describes Masashi as “fatherly”, which is odd enough given the age difference. That might just be symbolic though (a bit of a Jungian influence on the part of the author?). It really doesn’t seem like the MC has ever had a normal/healthy relationship of any kind with a member of the opposite sex, father figure included.
I don’t know how I would feel about a Masa RO at this point, but given Masa’s crush on the MC, his/she is probably going to be jealous when they choose someone else, whoever it is, and already seems to be jealous of Jun. Hopefully Masa doesn’t go off and do something stupid over it. Jealousy and unrequited love seems to be a big theme in the story. It might be Masa will love the MC no matter what we do, and will suffer consequences for that.