Someone should sue the Sorting Hat
Essentially, Masamune thought, the Sorting Hat was a fraud.
It was all very well in theory, sorting kids by their personality traits; very two-dimensional, of course, and divisive, not to mention bloody fucking stupid putting all the ambitious people from nasty backgrounds in one place. Masamune is not quite sure how nobody thought the whole idea of Slytherin was terrible long before it went repeatedly wrong, but who was he to talk? He was a Slytherin himself, and he knew he belonged there. It wasn't something he was particularly proud of or wanted to spend seven years of his life dwelling upon, but it was a fact.
Where the system really messed up, though, was the fact that it didn't even work. Masamune deeply suspected that it was at least 50% self-fulfilling prophecy even when it did, and the rest of the time... Historically speaking, Peter Pettigrew was hardly what one would call "brave".
And Ritsu...
Well, Ritsu hadn't proven to be very loyal at all in the end, had he?
Masamune would be the first to admit he wasn't a very nice guy. Originally when Ritsu had confessed to him, it had just been for fun, playing the naive little Hufflepuff - but he was the one who'd ended up getting played. Ritsu had hexed him and run off to America, of all places, and then Masamune hadn't known what to believe, between all the rumours and the discovery that he was maybe a bit more invested than he'd thought in their sham of a relationship.
But now Ritsu was back, and he was working for Masamune, the game was back on, this time with no House affiliations involved. Masamune wasn't going to lose again: he was going to make Ritsu admit he loved him, no spells, no potions.
And this time, he was playing for keeps.