I just started new book and we had first random encounter, which took whole day and it is not even finished!
Our scout found oni assault camp waiting and decided to do with their own hand. After hours of planning, they tried to sneak in charm the leader. But the leader hear one player cursing and started to blaming his followers. While everyone lined on thin path, sorcerer couldnt resist and boom. Surprise and boom again. Those who were still alive, were fastly put on ice or sleep by witch. They killed everyone but one, who was then charmed for questioning.
She was first one to drop, so she didn't know what exactly happened, but when she was "revived" and charmed by pc, it don't need to be an einsten to quess. So her first words were: "I surrender."
For her motivation, I picked blindly random word from dictionary, which was gossip. So, players now had prisoner who gladly told them everything, as long they had something with same value to tell back.
Now they had moral dilemma how to continue. She was clearly not safe to release but they didnt have heart to kill her either. After my players used many hours to make their mind, they thought if they should use Amatatsu sinet to turn her into ally as they used it to Zaiobe.
Second problem was they did not want awake every oni this side of planet. So maybe if they open the box in another box. In a 'virtual' sandbox universe. They consulted with npcs of caravan if it was possible. At Goija I said that it could be done in theory. Either at Adabar's safe or at dream under starry sky at starday.
At Ameiko I decided that she should be preparing to be future leader of nation and make decision and carry weight of them. So she decided to trust the plan.
So. Goija made sanctuary under power of Desna and those who supported the idea, went to sleep together. I gave the player who took part dreamy visions with meeting of Desna.
While those keeping guard I gave feeling of something big has happened.
Now, what really happened?
I decidee to left it to next day as most players were too tired to continue or pay even smallest attention.
But also, i really like to get some suggestions.
Well, just to get something out of the way... in the AP as written, I don't think the Amatatsu seal can turn an enemy into an ally. (For example, it doesn't change a person's alignment.) And I don't think the seal can work in a virtual universe. But if you've already allowed it to do that and the players are happy, then that's fine, it's your game after all! :)
What sort of oni is the new member?
Is Zaiobe still with the caravan and still an ally?
(Also, who/what is Goija? Is that Koya, the priestess of Desna?)
So, some ideas:
1. This could be a big thing, like redeeming a demon in Wrath of the Righteous. You could have a whole arc about the oni trying to be good, struggling with temptations, not being trusted by people etc. (A possible tragic-but-happy ending here might be for her to make a heroic sacrifice to save a PC, so she dies, but she reincarnates as a kami.)
Also consider that a lot of the kami and many mortals won't trust her, and most of the oni will want her dead.
2. Depending how you had it work with Zaiobe, this could be a dangerous development. Maybe the oni is lying (or maybe she's honest now but will backslide later). If the oni is now part of the imperial family, she might conspire against the party to get herself onto the throne.
(Depending on her oni type, her personality and the tone of your campaign, you could combine either of the above with a humorous running plot in which she keeps gossiping to the wrong people and getting the party into funny/awkward/dangerous situations.)
3. Maybe the seal only worked on her in the first place because she's not a fallen kami, she's an oni who used to be a human spirit (like Anamurumon). This could make her important to the endgame; e.g. maybe she can give a PC the ability to harm major oni in the way the royal weapons do, or she remembers useful secrets from her past life.
Our group is actually doing something similar, though not with an oni (that wouldn't work for my particular playstyle, but you do your thing!)
For whatever reason, my party became oddly attached to Slugwort, the ogre in the basement of Brinewall Castle. They managed to pretty easily dupe him during their first encounter and talk him into turning Kelda over to them, and then they just happened to pass through again later on to bluff him into helping them, and eventually they just realized he was too stupid to truly be evil (it probably didn't help that I began to roleplay him a bit like Sloth from the Goonies after their repeated successes.)
So, using the very Wrath of the Righteous rules Uqbarian brought up, they decided to bring Slugwort along and attempt to redeem him - and they've actually been pretty successful, managing to bring him to Chaotic Neutral.
We just finished Night of Frozen Shadows, and the party managed to convince Helgarval - the cassissian angel - to remain on and take Slugwort under his wing (I changed Helgarval to be an angel of Kurgess since I found back-to-back books featuring former improved familiar outsiders of Desna to be really obnoxious. I played Helgarval up very much like Kormac from Diablo III - lots of outbursts like "GLORIOUS!" - really playing into the cassissian's low intelligence, where he may have perfect memory, but he has no tools to put any of the pieces together and figure out what anything he knows actually MEANS.)
So now we have our 6 Intelligence angel of the god of strength and competition trying to help make our 3 Intelligence ogre Good-aligned. It's like the blind leading the blind, and it's hilarious.
Book 4 of the Hell's Rebel AP, A Song of Silver, has a gallery of NPC's that work in other AP's because of course it does and that's what we all expect to happen.
The logic of that aside, one of the NPC's is a reformed oni named Hirakonu for the Jade Regent campaign. I stopped reading once I realized what was going on since I am playing that AP right now, but you might want to check it out for ideas for how an ogre mage can, logically, end up supporting the party.