Hojo
If you have been waiting for a time to extract revenge on Hojo for his actions when you invaded the Shinra HQ, now is your chance. We find Hojo getting ready to use the Sister Ray mako cannon on the Northern Crater when we confront him.
He appears with two Sample based enemies but leave these along, they give no bonuses and Hojo will just revive them. Instead cast haste on the party and use deathblow and other strong magic to take Hojo out. He is invulnerable to gravity though, so be sure not to use demi skills.
After you defeat him you are thrust into another fight against him.