After who knows how many time loops, Jeanne Alter's run out of material. Even BB wasn't expecting it to take this long so she decides to throw Alter a bone and let her sell porn at ServFest, which should be a guaranteed win. Alter refuses, so BB traps her in her NP. Alter figures this is going to be a "I won't let you out until you draw the doujin", but actually BB summons a copy of Gudao to bang Alter until she gets in the mood to cooperate.
That's the setup until the end, where there's a reveal. By then Alter's forgotten her original goal and descended into an endless loop of sex with the Gudao copy, while BB snickers her real plan was to trap Alter in the loop forever so BB could claim the real Gudao.
If you want, you could think of this as answering the question of what happened to Jeanne Alter in Summer BB's Bond 10 CE.