The MV was nice to watch. Sets the tone of the song just right for me, the solo scenes were superb. Though I would've liked some more focus on the third row than what they were given. I also think that the fourth gens should've just been the ones crying and the senpais were to help them get out of their depression, I think that would've made it have a bit more of a story. And now that Seditious has mentioned it, the "hey"s don't actually feel out of place at all. Considering their placement in the lyrics, after "kurayami wa" and "fuan to wa" (both can be perceived as negative words; though "taiyou wa/yo" doesn't really follow this), the "hey"s could easily be the voices from their friends letting them know that they're not alone only to be being drowned out by the individual's negativity (stemming from it only appearing in two lines of the chorus). So I think it makes perfect sense to have them.