I swear it's "bokutachi" because I, well, I can usually follow the lyrics at the bottom while they are singing, but, I'm far far far from skilled in Japanese.
But I thought it was bokutachi too, because for bokura they always had the hiragana after "boku" so...yeah, thats how I remember things
Hiru says that it says bokutachi too, and he can actually read so...maybe...she just...forgot? I don't know. Kind of changes the meaning of the sentence a bit doesn't it?