A War Across Time: Devas and Rakshasas

The Sundering required the forces of good and evil to adjust their tactics in their pursuit of influence over the Prime Material. Many of the soldiers in the cosmic war chose to be bound to the world, forever surrendering their right to return to their home planes in exchange for the right to remain on the Prime Material.
These spirits instead are reincarnated over and over again. Good spirits take the form of devas, while evil spirits take the form of rakshasas. The two are reincarnated slightly differently, but it is their first acts which distinguish them most clearly.
Devas are reborn as young adults in holy places, with only dim memories of their many previous lifetimes. They are often adopted and raised by the ordinary mortals that tend such sites, with the result that most devas have a close affinity with a church or other holy order.
Rakshasas are reincarnated in places of darkness and corruption, with continuous identities and memories. Emerging fully formed from its time of torment in the Shadowfell, with all its powers intact, a rakshasa's usual first act upon returning to the mortal world is to slay every sentient being it can find until its rage is satisified and it is certain there are no possible witnesses to its return.
The two spirits are constantly on the lookout for one another, and seek to destroy the plans and physical forms of their timeless enemies whenever possible. Some devas believe that a rakshasa spirit can be redeemed, and will become a deva. The opposite process, where a deva is tempted to darkness and becomes a rakshasa, has been theorized as well. Obviously, documenting cases of either one is problematic for mortal sages. One thing that is certain, however, is that the possibility of conversion does sometimes lead to situations where prisoners are taken in the war across time.