You can only teach John Rank I skills, it's that Aura needs to have the Rank II version of the skill to teach it to him. The skills you teach him will get bumped to Rank II after the Reverse Summoning Ritual. So, for example, if you get Light II then you can teach him Light I and then after the Ritual is cleared the skill will be upgraded to Rank II. Martials work the same way, if you teach him Pierce I it will upgrade to Pierce II after the Ritual.
You can learn Slash 3 from Hero John (after Reverse Ritual), Pierce 3 from Loraine after the mission involving her and Roland, Rampage 3 from the knight outside the Knights fortress after beating him and giving him time to develop it, Light 3 from Gabriel after talking about the Reverse Summon ritual, Horror 3 from James after getting a high enough approval (and having enough Vice), Summon Slime 3 from the Slimey club, Assassin 3 from the cultist in the Demon Cult bar, Seductive stance 3 by upgrading it in Aura's mind area (requires high corruption and losing another skill), and either Fire, Thunderbolt, Storm, Tremor, or Splash 3 (you can only get one) from the elite club by both completing Reverse Summon ritual and mastering all lower tier spells from that element.
I think they are referring to slime Bonding 3, the spell itself only goes to 2.
There are actually a couple of distinct victory endings on top of all of the minor changes based on your choices. I had a playthrough with a very lewd Aura (30+ lewdness) but actually got the "pure" victory ending where her life hasn't changed drastically. Surprisingly, there were multiple dialogues and a scene acknowledging how lewd Aura had gotten, which I thought was great.
* Ok, so it seems that a lot happens after this reverse summoning ritual where those retards will try to taking down the goddess. It's really getting better and better...
I have to ask, though. Do you remember how far you went in transforming mental rooms? e.g. As the "appearance room" (upper right corner in the "Entrance room" is rather representative from all the changes in the other rooms, what did you got changed? shortened skirt, shoes makeup, hair style? and so on
I think that as long as you don't go into the final major room, you can get a mostly pure ending. If you go into the second major room then Aura will still have some changes, but if you can do it before leaving the first major room then you get the most pure ending.
This is a rough outline:
Wow, I was more or less expecting there to be several possible endings and variations depending on the choices. After my first playthrough, which ended with Arwin or Aura as his brainless puppet and Richard as Princess Crown's plaything, there was an ending where she ends up as Roland's slave, as one can imagine from the previews in the op, and of course one where Richard and Alicia should be victorious, but Aura the Demon Queen? I didn't see that one coming.
