No.350
Ignoring any theory about Madotsuki's relationship with him, I see him as the older brother's friend you find in shoujo. You're crushing on him, and may be you push social boundaries a bit, but you'll never really be intimate with him. He's nicer and warmer to you than anyone else you know and it makes you giddy but it's nothing to him.
When I go to see him it doesn't feel like I'm escaping a world of chaos. I've always without thinking phrased it as 'he's letting me visit'. If the game won't take me after multiple attempts, I treat it like Masada wants some space. But if I arrive on that staircase I think he's longing for company.
Putting a theory to that I guess the teacher position suits best. Nothing sexual, he never enters the bed with you and it's reasonable to assume he lets Madotsuki rest there without romantic connotations. He's concerned for her, which is why he lets her come to his home, use his bed, but he also needs someone because his home is so devoid of life. There's an empty seat that stares at him when she's away.
I feel, the piano being big as it is, that may be he was a performer at some point. Its size is daunting but tempting to idle fingers. It guides his way amongst the stars like a control panel though in the end he still crashes and is trapped there. He prefers to play the piano than to see the empty chair.