You don't need to unlock this shot: Janus, Diam and Rihm know it since the beginning.
You can use it if two of these players are on the field. You don't need to unlock this shot: Mercury, Metron, Zell, Janus and Heat know it since the beginning. You can use it if three of these players are on the field. After you unlock it, this shot can be used with/from Nelly (Girls' Team) too.
You can use other managers as partners, if you like. After you unlock this shot, Miles can use it too. After you unlock this shot, Stonewall can use it too.
After you unlock this shot, Axel can use it without Canon, as a normal lv.3 shot.
