Could go either way, honestly. Her focus is mainly on Sakuya though, never the guy she's straddling. Over time, she could become bi-curious, but she's most likely just hot for Sakuya in action.
You could also just view it as Remilia wanting just to watch some hot action with her focus on Sakuya(or just any girl). I mean, for the part, that's how regular porn works even if it isn't PoV porn. Guys would just ignore the Dude in the porno video and just focus on the hot girl getting plowed.
