To unlock Cloud Strife you must first unlock every other character. You must beat Musou mode with every character on hard mode. You must max out every stat on every character.You also need every 4th weapon in the game. Then with Fu Xi beat the last Musou mission in 7 minutes or less. Then Cloud will appear defeat him. He will then ask you to help him fight Sephiroth. DO NOT LET CLOUD DIE. He will join you and you pick if you want him on Shu, Wu, or Wei. He will be in every fight the leader is in and he will duel Sephiroth at the end all the time. His attacks are as followed.

Charge 1 - Blade beam
Charge 2 - Climmazard
Charge 3 - Braver
Charge 4 - Meteor Strike
Charge 5 - Huge Slash
Charge 6 - Finishing touch
Musou - Omnislash
True Musou - Knights of the Round Table

He has max stats and good reach, speed, musou charge and jump.