It explodes when they run into it. If they super jump over it you have a good amount of time to react.
Also just finished story mode in the hardest difficulty, Kamui is stupid and his command grab has way too big of a hitbox. In the match winning battle I was so shaken up I kept dropping EVERYTHING.
Ironically in that same fight I discovered a glitch. If he uses his counter-burst and the attack that hit the counter kills him. It starts a round 1.5 where you're in the same health and he has max health, your healthbar doesn't drop but your health does. Regardless of who wins that fight round 2 will start without anybody getting a win.
I will upload video shortly.
Video uploaded: http://youtu.be/0I2T221gusk Glitch at 1:00
