Not-Quite-Canon Verse: So named because while I hesitate to call Koschei canon in any verse, this one comes as close as you can. The Master is returned to life, with memories wiped; Koschei ensues. He fights; he never figures out who, exactly, he is; he slowly loses hope. Until the day the Dalek Emporer takes control of the Cruciform. Alongside the terror, something cracks through that iron door in his mind and the Master comes back. And he runs. From there on, we follow canon. This verse is where everything branches off from initially, but doesn't get poked at much, mostly because the mun made the mistake of coming to adore Koschei and now the idea of him turning back into the Master makes me flail.
Post-War Verse: Also known as the verse that needs a better name, please. Similar to Not-Quite-Canon Verse, until the day the Cruciform is taken. Because whatever manages to crack through to his memories, in this verse, doesn't get through. Gallifrey dies. Koschei, by some fluke, escapes and survives, running off with his TARDIS and enacting a hunt for anyone else who managed to survive. This verse is slowly coming to be poked more thoroughly.
Memento Mori: Only a couple of years into the war, Koschei goes out on one of his semi-regular "break the locks on the TARDIS and take off for a couple of days" trips, and happens to end up in London, where he runs into
a man who used to be the Doctor's hand. The two are drawn to each other immediately; both broken to some degree, with a shared past neither of them can quite remember. Koschei invites the other (who, evenutally, aquires the name Theta) along, and in doing so officially becomes a renegade and a deserter (as well as a thief, taking the TARDIS with him). The two travel together and slowly grow close. This verse tends to be Koschei's default; it, and most of the verses spun off of it, also take place in the parallel universe.
As If It Were a Commodity: After travelling together for a few years, Theta and Koschei are found by the Time Lords and returned to Gallifrey. Both have their memories completely removed; Koschei is kept to plan and to fight, and Theta is kept because they didn't want him loose. While things are falling apart around them, Koschei manages to escape and stumbles across Theta. The boys find their way to the TARDIS and leave Gallifrey, now with no memory of life beyond their secluded existences, and learn to deal with life and each other in a new way. They also spend a lot of time reading out loud.
Protect Me From What I Want: Though Koschei struggles with the drums and the Master in all verses, in this verse, he can't manage to keep them down. After
Theta's regenerated twice and they both realize that every regeneration gets worse, Koschei becomes obsessed with finding a way to fix him. Finally, he finds him a new body as a way to, if not fix him completely, reverse the damage the regenerations have done. A body that can heal itself, one that never dies. The fact that Jack Harkness still occupies this body doesn't really bother him. Theta shares a body with Jack and a manifestation of the Doctor that's more than a little sketchy, neither of whom are in favor of Theta staying with Koschei; this does nothing to help the drums that just get harder and harder to control.
Drumsverse:
Theta and the TARDIS conspire together and manage to pull the drums from Koschei's mind. You would think this would be a good thing. You would be wrong. Now Theta has the drums and keeps on running away; and Koschei follows after him, trying to get him to stay, and tries to adjust to a silent existance in his own head.
Memento Mori (Aftermath): After
Theta's death, Koschei travels alone for a while, somewhat recovered but still grieving. It's not long before he finds his way to the Inn, one of your friendly neighborhood pandimensional meeting spots, where he finds Theta, pulled in after his death (as the Inn is wont to do) and much healthier for it. They continue to travel, living out a quiet life together.
And So Be Healed (Happyverse): Once more in the Inn,
Theta finds a man from another universe, Cowslip, a healer (who, coincidentally, looks exactly like Theta) who fixes him. Though Theta has to return every so often for "treatment", he's far more functional than he would be alone. There's a lot of change, a lot of redefining of the relationship, and a lot of issues to work through, but eventually, Koschei and Theta get a happily ever after. This verse eventually goes from calm and sweetness to domestic vigilantes with cats, though only after several centuries together.
Dismantle the Sun: This verse takes off after several centuries of Happyverse. For ages after
Theta is fixed, the drums and the Master have been a nearly nonexistant entity in Koschei's mind, only bad enough to catch his attention every so often. On one of those unfortunate days during a trip back to the Inn, someone gets into his mind and aggravates them, bringing them back to full strength. Determined to keep from hurting Theta, Koschei runs, though the seperation only makes the drums worse. By the time he's convinced to come back, criminal is the best term he can afford himself. Theta's backslide during his absence keeps him there despite his fears, but between Theta's brokenness, Koschei's guilt, and the barely controllable presence of the drums, their happy life together is almost impossible to recapture.
Boomverse:
Theta finds a way out to Gallifrey, and the Time Lords end up keeping him there. Koschei finds out where he's gone and follows. The Time Lords attempt to use Theta as bait to reclaim their soldier. Bad things follow. Worse things follow that. Eventually Gallifrey explodes; this time, it's not the Doctor's fault; there is massive breaking on Theta's part and massive rage on Koschei's.