You mean MyonHime? Eh, I'm not particularly attached to it. Personal UdoMyon tendencies aside, I've always felt like Youmu screams aro-ace, both in Touhou in general and the Purvisverse in particular. I do plan on at least checking romantic history once it became prudent to do so, but I would be surprised if there was any. (I asked about Reisen at the beginning of the game for this reason; the response to that query just further bolstered the aro-ace idea.)
Also, as cruel and blunt as this may be, Kotohime's kinda sorta dumb, and I have a hard time seeing Youmu going for that.
But we'll see! I do feel a bit bad for her, so I don't intend to give a flat no, at least. Most likely I'll leave it as "we just met 8 hours ago, let's take some time to get to know each other better" and leave it to the currents of postgame/future games to decide their fate.