Taken from Gods Eater Burst's database:
An Aragami resembling a human fused with a butterfly. Emits rays of light from its forehead: baffles Gods Eaters as it floats seductively through the sky. Thought to have first appeared along the Mediterranean coast. Hard to inflict serious damage while in mid-air, so shoot it down, then attack it with one's sword. Launches long-distance homing attacks as well as debuff attacks, so take advantage of the terrain and stay mobile.
Sariel is a powerful aragami. You have to keep moving and firing with your gun because most of her attacks are homing. As much as possible, bring 2 gunner allies with you (like Kota or Sakuya) for better survival chances. Never stay away from your allies and fight it alone. If this is not an option, then fight it; but still use your gun. Try to use blade only when she is down.
Fire, Ice, Spark