As a whole, what I'm taking away is that only the most basic ideas of the mythological concepts we're working with have actually been preserved, and it's more accurate to say that we're working within your mythology, which has had some familiar terms slapped onto it.
This is indeed true, and I'm sorry if that wasn't clear before. I try to not be restrictive, but with so many mythologies put together, I have to make some modifications to make sure they're all consistent with each other, and with my universe. For instance, none of the mythologies' creation stories can really be true, since planet Earth is still billions of years old, and humans and spirits gradually evolved on it. Additionally, my own characters and the characters of the co-GMs have their backstories too, and we obviously have to make sure the setting is consistent with these backstories. But as you said, we're still trying to preserve the basic ideas and themes of the various mythologies we're using, so that they're at least somewhat recognizable as their real life counterparts.
All in all, I'd suggest that you don't try to put too many details into your character's backstory until the actual game thread is up, at which point all the information will be given to you. Then you'd know how to work within the setting's limitations.
Just as an example, you can't blame me for assuming that Tiamat is dead, given that the primary point of her existence in mythology was to be slain by Marduk and used to create the Heavens and Earth from her corpse.
Oh, right, I forgot about that. I was looking for dragon-like chaos monsters in mythology that have parallels with one another as the leaders of the Reclamation of Chaos, and wanted seven of them due to the game's numerological theme. Some of them are dead in their own mythologies, e.g. Tiamat and Yamata no Orochi, but I still wanted to use them, so I made some changes. I won't blame you for expecting more mythological accuracy, of course; I should've made things clearer in the beginning.
In any case, my character concept is thus when stripped down to its core concepts: a person bonded with Tiamat, with powers themed after oceans, life, and chaos, with a Lovecraftian bent that portrays Tiamat as some manner of chthonic broodmother of the deep sea.
Regarding finer details: I would like my humanoid character to be an oceanic explorer and/or marine biologist, that may have encountered Tiamat in the deep sea, possibly when the Seals were undone. His exposure to chaotic magic, particular Tiamat's has warped his body to be inhuman and fishlike, which he keeps secret with such implements as a long coat and an eyepatch.
These ideas are fine. One thing to note is that even if your human character's body is mutated by magic to become fish-like, his soul is still recognized as human by the Seven Seals, so he still functions as the human half of a Soul Pact needed to bypass the Seals' power restriction. In fact, quite a number of humans have had their bodies changed by magic, so they don't look fully human anymore.
But as I said above, I suggest you refrain from adding too many details to your character until the game thread goes up, so that you won't end up adding something that doesn't work.
