There are two boss fights with Blueno: one in Chapter 9 and one in Chapter 10; you'll only get this in the Chapter 9 fight, and this is the 2nd hardest event attack to pull off in the game.
Bring Blueno's health down to about 2/5 (His lifebar shows one long bar and one short one, so basically get him down into the shorter bar), and then totally stun him so he's on his knees AND he'll have two stars spinning around him: a yellow one and a red one. This can be very tricky as he is fast and he usually does his Rankyaku/Tempest Kick attack in threes before he finally stops. Try using the Square, Triangle, Triangle attack to do this. When you see the R1 indicator, hit it to trigger the event: press X to avoid one attack, then push the Left Analog Stick right plus R2 to avoid the next attack, and then spin the left stick counter-clockwise (I press my palm to the stick to make faster rotations) to finish up.