As a last resort, what if you asked your dad to join you on the trip? (I'm guessing the most important thing here is seeing the band.)

If he wants to go, then plan everything. Itinerary, hotels, activities you like and activities he would like. I'm not even saying he needs to go to the actual concert. This would show him that a) Japan is a really safe country and b) you are very capable as a solo traveler going forward (if you want to do more solo travel or study abroad) because you took charge of the trip.

If he doesn't want to go, he might see the fact that you asked him as a sign of your maturity and be more supportive of you going alone (I'm hoping this is what happens and the reverse psychology works)

When I was in college, I made this point to my father by going on an international trip with him that I planned. He still doesn't think I'm capable of much, but he never questioned my solo travel after that. He also doesn't ask to come anymore - he got tired because I had him walk everywhere.

For the record, I think you're an adult and you should go no matter what, but I also understand living with overprotective parents as an adult and not wanting to upset them.