Board Thread:General Discussion/@comment-6192846-20150613141203/@comment-26871067-20150821164558

67.66.95.88 wrote: Olivemeister wrote: I just realized the incongruity of Irina apparently being the singer of FML despite not being a Rin character has a stupidly simple explanation: she's using a Rin as a medium. Can't believe how obvious that should have been. Of course, it's not confirmed that it's Irina singing FML but the implication is pretty heavy. More likely that Mothy just didn't have Iroha at the time. :V Why not both?

It's definitely the case that he didn't have Iroha planned to play Irina, since she was released 8 months after FML was uploaded. I don't think she was even announced at the time. But that doesn't mean that there isn't an in-universe explanation for why the singer appears to be different, and using a Rin as a medium makes sense.