Sakana continues to push forward on his idol dream. Nice to see, honestly.
And inviting Mint as a special guest is just a good PR move in general, there will most likely be people discovering Phase just because Mint's present in a concert with them. Unhealthy speculaton about her joining as an invader comes as a bonus.
Well, that apparently was because she thought she was getting a good deal - good enough for her to knowingly ignore the glowing red signs(as a reminder, in her first announcement of joining a company soon she said, and i quote, "it looks like a scam but it isn't).
And yeah the clip above kinda suggests that she might have a slightly-inflated sense of her own importance.