I'm surprised that Ciel...

[Miraploy]

I'm sure that some sort of fusion and memory exchange occured.

I'm sure you are wrong on this one. There is no "soul fusion" when Roa invades a host, he just takes over. from time to time the other soul seems to "wake up", as it happened with SHIKI (but I think that never happened before) but the souls stay as separate entities.

I never said anything about the soul. We don't understand the Tsukihime idea of the soul. I only said fusion and memory exchange. Which is accurate.

Remember, Roa loses part of himself every time he bodyswaps. Why? Because he takes in parts of the host. Why else would he choose a wealthy host if he wouldn't retain any of his memories?

I don't fully understand what you want to say here. Are you saying that Roa takes rich families' baby because of their memory? I think it's said very explicitly in the game that he takes rich babies as their host because that makes the job of exterminating the whole town a lot easier than being a no-body's son/daughter.

I'm saying he wouldn't be able to use his new body's power and influence if he didn't have any of the new body's memories. I think it's pretty clear from both Roa's experience with SHIKI (when he taunts Shiki in the Roa personality), and from the description of Roa's losing himself that Roa does absorb all of the host's personality/memory.

The question is whether that is reciprocated on the host side.

Also Shiki's experience in Ciel's route is very informative of the way that Roa takes over. It's not a sudden change in command, nor is it a sudden shoving aside of Shiki's will. Roa is a combination of desires and memories. Also Shiki does get Roa's memories, he remembers his experiences as 17 in France. So even if there wasn't a complete merger, there was a partial merger.

That was different, and it as not a merger. Because of the kind of bond Shiki had with SHIKI (remember that Shiki sometimes saw "himself" killing long haired women?), Shiki was able to get into Roa's memory and see his/her past but there was no kind of merging/fusion of souls. It's important to take note that Shiki does not have all of Roa's memory, he has like two or three of them if I remember, but from what you said I got that you said that he gets all of Roa's memories, which doesn't happen.

[/quote]

Can you read mate? I never said anything about a fusion of souls. I said a partial memory/desires merger. Which is obvious from Shiki's experience. His sudden desire to rape Kohaku, etc some of his actions afterwards, were Roa influences.

chasmirror, does it say anywhere if the soul normally dies when Roa invades?

[abscess]

I never said anything about the soul. We don't understand the Tsukihime idea of the soul. I only said fusion and memory exchange. Which is accurate.

Let me answer with another quote:

http://typemoon.wikia.com/wiki/Soul
A soul (魂, tamashii?) is a record, the memory the world has; it is the second element. An existence independant from the body, it doesn't belong to the material world like the body, but to a concept above it, on an astral plane. It is the source of energy of a spiritual body.
Memories and Magic Circuits aren't stored in the body, but in the soul.

Can you read, mate? I quoted that same article before in other discussions we had.

I'm saying he wouldn't be able to use his new body's power and influence if he didn't have any of the new body's memories. I think it's pretty clear from both Roa's experience with SHIKI (when he taunts Shiki in the Roa personality), and from the description of Roa's losing himself that Roa does absorb all of the host's personality/memory.

The question is whether that is reciprocated on the host side.

I don't remember ever having a clear explanation of it. From what I get the past user's SOUL (because that's where the memory IS stored) sometimes "wakes up" a bit and that's the moment when the information exchange could take place, but as far I know there is no actual fusion of SOULS. Perhaps, as you said, there is an exchange of information in such a way that Roa takes part of the past user's personality for he is an incomplete version of the original Roa, but when SHIKI is in control I don't remember SHIKI talking about something other than what he, SHIKI, craves for.

I'd say there is no reciprocal info exchange. Ciel only remembers Roa-Elesia's doings, but doesn't remember any past events that other Roas could have experienced. That would happen mostly because of Ciel's supreme magical prowess she possesses.

I doubt there is any need for Roa to have full control of the past user's memories or access to them and there would be no actual NEED for him to have it to be able to use the magical circuits of the SOUL (because, you know, those are IN the soul too, like the memory, remember?).

In order for Roa to use the magical abilities of the past user, namely magical ones, the other guy's soul must stay somewhere so Roa can access them. If he copies the neded data into his soul and discards the original or has the original at hand to access it every time he wants to use those circuits is something I don't know, but that shows us how powerful Roa was but is never really shown in Tsukihime.

[chasmirror]

The question is whether that is reciprocated on the host side.

chasmirror, does it say anywhere if the soul normally dies when Roa invades?

The Dokuhon doesn't specifiy anything about that. Sorry.

As for the host, it does not seem the case, especially with Ciel. She mentions in the Tsukihime game that she was consciouis and kept telling herself to stop the killing while being possessed by Roa, which would not have been possible if memory absoprtion went both side.

What we can assume is that when Roa takes over, the host usually is consumed by him. In the end, there is only one personality, a mixture of the host's and Roa's. This is why Roa personality is stronger in Arcueid and Ciel routes, whereas SHIKI personality is stronger in Tohno house routes. Since Ciel is the only one that is known to have preserved her soul after Roa, the others must have either completely absorbed or expunged by Roa.

Shiki does see some of the Roa's memory and feeling like in a dream-like state, but this is mostly like due to his connection with SHIKI. The closest explanation is how Shiro saw Saber's past in Fate, or how Rin saw Archer's past in UBW. The connection allowed bits and pieces of memory and emotion to flow between the two separate individuals.