If I can defeat you here, the fal'Cie plan will fail. I will use all my remaining power! I will set you free!
My will is my own! My will is my strength!
In the first half of the battle Raines switches between Offensive Shift, Defensive Shift, and Recovery Shift, which are the enemy equivalent of the Commando, Sentinel, and Medic roles. During Offensive Shift he has access to a powerful physical combination attack against one character and can cast Ruin. During Defensive Shift he uses Guard to reduce damage, and during Recovery Shift he uses Cure and Esuna.
When approximately half of his Hit Points have been depleted, Raines will use Metamorphose, immediately followed by Seraphic Ray, which deals high damage and removes all status effects from the party and himself. From this point on, Raines does not signal to the player which role he is currently assuming, but still uses Offensive Shift, Defensive Shift, and Recovery Shift as well as two new roles, analogous to Synergist and Saboteur. During Offensive Shift, he gains access to Ruinga, and his physical combination attack becomes more powerful.
During Recovery Shift, he begins using Curasa instead of Cure. During his Synergist role he casts Protect, Shell, Vigilance, and Haste on himself in quick succession. During his Saboteur role he casts Poisonga, Deprotega, Deshellga, and Dazega. He will use Seraphic Ray periodically; one can tell if he is going to use Seraphic Ray as he will uphold the guard position directly beforehand.
Like many bosses, Raines will cast Doom on the party leader if the battle exceeds twenty minutes.
Staggering Raines is an effective way to defeat him, thus attacking fast with Ravagers in the paradigm is a good idea. When Raines uses his Defensive Shift it is a good time to heal. Saboteurs can be deployed to give him status ailments: he is most susceptible to Slow, but will heal any status abnormalities in his healing paradigm with Esuna.
If he enters the healing phase, the player should switch to Relentless Assault and attack him until he switches to the offensive phase. If he goes back on the offensive, the player can switch their paradigm to include a Sentinel and/or Medic and continue attacking, as he will probably be targeting the Sentinel most of the time.
When Raines is either nearing the stagger threshold, or is already staggered, and if Lightning is the leader, she can summon Odin, and remain as a Ravager to attack Raines. Once the Gestalt Gauge is filled, the player should ensure Raines's chain gauge is still high so that Odin and Lightning can devastate him in Gestalt Mode, repeatedly using Stormblade and Razor Gale before concluding with Zantetsuken, because Raines's chain gauge should already be running low. Ideally, this should defeat him, or at least leave him close to defeat.
Another good way to defeat Raines is to exploit the Commandos' Launch ability. The idea is to stagger Raines, and then pummel him with launched Commando attacks. It is good to include Sazh as a Ravager for his Synergist beneficial status effects, and only attack when the party is fully enhanced.
A good battle team for this strategy is Lightning (as leader for a summon), Snow (or Fang, but her RAV role will need some development) and Sazh. This provides two Commandos with Launch, while Sazh provides the best Synergist statuses for the fight. The recommended paradigms are Protection (MED/SEN/SYN) as the active paradigm, plus Tri-Disaster (RAV/RAV/RAV), Aggression (COM/COM/RAV), Entourage (MED/SEN/RAV) and Thaumaturgy (MED/RAV/RAV).
Raines is easier to defeat while he is still in his first form. Ideally, the party will stagger him before he metamorphoses and once he is staggered, the two Commandos and one Ravager combo can defeat Raines, even if Raines has full Hit Points, before he recovers. By keeping him launched, the two Commandos prevent him from guarding or launching a counter attack.
The party cannot launch Raines while he is guarding, so the party should finish filling the chain gauge immediately after he finishes defending, giving the party an opening to both stagger and launch him. Raines's guard periods cannot be avoided, but can be used to fill his chain gauge. If the party are on the verge of staggering Raines while he is still in his guard phase, they can switch to Protection to avoid pushing the gauge past the stagger limit.
Behind the scenes
Defeating Raines before he uses Metamorphose makes the subsequent cutscene nonsensical, as he will suddenly have a set of wings that appear out of nowhere.
Despite having an enormous clawed arm, Raines kicks more often in his combination attack. He will only slash with his claw once per combo.