Touhou 12 will feature pairs, just like IN.
The first girl will be the player, just like any Touhou game. The second one will be the assistant and will act like an option, and will only be on screen when your power is level 2 or above.
Bomb system will be just a mix of MoF/SA and IN. You lose a power level when you bomb, and the bomb is performed by the player. However, when you counter-bomb, you'll lose up to two power levels, and the bomb will be performed by the assistant, consisting in a more powerful and longer bomb attack.
There will be 4 pairs available:
Reimu/Yukari
Marisa/Mima
Alice/Shinki
Komachi/Siki
Yeas, both Mima and Shinki will be back. I feel it in my bones.