A Little Help Understanding Please?

Ren's vessel = someone who can hold the spirit of Ren (like his next body to jump into). Ren is what Garai became after being stuck there for a millennium (he went completely crazy). Not a reincarnation so much as a long continuous consciousness stuck there...

Ren is not a raincarnation of garai like kou and touya of their past lives. Because he did something taboo. he almost could not remember luche or tarupa because of what he did. For all intense and purpose he is garai but not complete like kou or touya.

I can't really explain the third because it would confuse you but basicly tarupa was never with garai to begin with when his soul past on to a new host. Tarupa was inside the jewel sealed but then kamiyo devoured the dog who became a monster after coming in contact with the jewel. Ren and tarupa we're together just not in contact with each other for they we're separated. We don't know how the jewel got stuck on the branch but it did and kamio came into contact with it when he devoured the monster dog. And then when he found kou he fully merged with tarupa when you touched the gem and said u can never b a true clansmen. As far as we know garai 's memories are inside jun but garai himself is gone because he was killed by raki. However we saw prince Ren enter kou and then Jun started drawing the shima warriors.

This is what my theory is hope it makes sense.

wait didn't ren enter jun when touya and kou destroyed ren and his barrier?? and that is why jun has all of garai's/ren's memories?? and they kinda get more 'unlocked' each time he comes into contact with tarupa's spirit jewel??

Yea but not garai he went with raki when he released him the resedue was left with fragments of memories that possessed Jun through you. Because when he pulled out the sword it went inside him and then into Jun. The memories of garai are plot between hazuki and Jun I think

This is my interpretation:
Garai performed a forbidden spell to save Raki's soul. He sacrificed his body to guard his spell, and over the years his soul degraded with time (he did whatever possible to make sure his spell was intact). This soul which resides under the kamio residence needed a medium in order to guard the spell. This medium = Ren's Vessel. Ren isnt a reincarnation of Garai but a vessel that holds Garai's degraded soul (thoughts, desires, and etc). About Tapura = Once a contractor dies, the beast within leaves the host. The beast is quite picky about its contractor (it doesn't care about family ties and etc, example: Tohya (not touya), he was an outsider who got Misura). Kamio is the sole contractor of Tapura. However, when Garai performed his forbidden spell the beast also suffered some heavy defects. Since Tapura is defective it is understandable why Kamio is having trouble accessing Tapura's powers and memories.

Hope this helps!

If Tapura wasnt defective, Kamio would've the memories of all previous Garai (there is no inheriting the soul, the soul passes on...example: the previous Raki was put to rest by Kouichi, but kouichi inherited his memories). The person who inherits the name Garai is the one who has Tapura. Just like the one who has Luche is Raki, and the one who has Misura is Tohya.

Hope this helps!

The soul does have the complete memory so when the body dies the soul leaves. TonHya tied his spirit to the sword. When TouYa took the sword he also got the TouHya soul and his complete memories.