They're called Tri-Attacks in the na version. You need to accumulate "resonance points", which are gained by performing hero actions that cross between the other two party members (the anchor line will turn blue when it's set correctly to generate a resonance point). The tri-attack itself is initiated with Triangle then executed with Square. All 3 characters essentially do a simultaneous hero action for only one bezel. It's pretty useful, and with enough resonance points you can easily carve through a room of 7+ enemies
Note that you'll lose stored resonance points by performing anything aside from hero actions that would generate resonance points.
I could go into way more depth if you like, not sure if you just wanted to know how to do them or everything about them.
Note that you'll lose stored resonance points by performing anything aside from hero actions that would generate resonance points.
I could go into way more depth if you like, not sure if you just wanted to know how to do them or everything about them.