We should also talk about how Tetia and Tartah are both fully radicalised in the silver Eve arc due to the experiences they have with outsiders: Tartah is fully radicalised since his arc started before hers. Custas and Eoleo, two outsiders who show Tetia and Tartah the nuances of society that the witches code dismisses and can't help. They both aim to help Custas and Eoleo. Tetia helps Eoleo by providing tents to the injured and by hiding him away from those guards in chapter 52. Tartah tries to help Custas by telling him that Dagda can be saved if they get him to King Ezrest, a doctor who can treat his injuries. Tartah and Coco also try to help Custas through other ways like providing knowledge and the flying gadget before the silver Eve festival.
What's ironic with Tartah and Tetia is the constant acknowledgement by Shirahama about how 'outsider like' they are as witches. What I mean by this is that both Tartah and Tetia have multiple arts or in-text acknowledgements of them being similar to outsiders. Tetia is compared to a princess, while Tartah is compared to a regular unknowing who can't use magic. Its even more interesting that these acknowledgements reflect their relationships with an unknowing (Custas) for Tartah and a prince (Eoleo) for Tetia.
I would also like to mention that Tetia and Tartah's relationship with outsiders lead them close to the brimhats. Tartah joins the brimhats to find out the truth and to help Custas. Tetia's connection with Eoleo is also connected to forbidden magic as the Ezrest family are descendents of healing witches, and the brimhats wanted to give the silvertree seed to King Ezrest. Ultimately, this makes Tartah and Tetia vaguely connected to the silvertree seed with Tetia's connection to it, probably strengthening over time like Tartah's.
Tartah and Tetia both break the witches code in the Silver Eve arc. Tetia learns how to use herbal medicine and apply bandages to patients injured by the curtain leech. Tartah brands himself with a truth spell and joins the brimhats. Their acts of breaking the witches' code are followed by the threats of the Knight moralis. Tetia is threatened by the twins but is saved by Richeh and Agott's quick thinking. Tartah is threatened to be sent to Adanlee, and the only thing he can do is leave pointed cap society.
As we know, Restys, Ininia, and Custas were all on a mission to deliver a bottle of silvertree seeds to King Ezrest. The brimhats are known to use the silvertree seed for their medicinal research. They most likely sought to give it to the king to form an alliance and discover forgotten healing magic. However, they failed to do this, and Resyts, after discovering what happened with Custas, chose to delay the mission. This means that the brimhat trio is likely to make another appearance in Ezrest. Not to mention that Tartah and Ininia now both have emotional ties left at Ezrest. Nolna is still looking for Tartah and chose not to return to khaln in chapter 90. The same probably goes for Galga and Atwert, who are implied to have stayed in Ezrest looking for Ininia.
Now we have Tetia who finds herself with Eoleo's brushbuddy. She definitely intends to return it to him whenever she is able to meet him next. This also means she will most likely travel to Ezrest using the window to try and deliver it. On top of this, tetia and the brimhat trio aren't the only ones with business left unfinished in Ezrest, but so is Richeh. Riphillin and Beldaruit currently find themselves stuck in Ezrest's Castle. With Richeh's arc focusing on staying true to herself and helping the people she loves, there is a high chance that once she hears about Riphilins' predicament , she would also have business in Ezrest to be dealt with. Also, Richeh's depictions as a Knight make me believe that she will help in saving Beldaruit and Riphillin.
All of these characters are now connected to Ezrest. It is possible that after this arc, we will have all these characters meet in Ezrest. This would mean that there's a high chance of brimhat/undecided Tartah meeting Tetia as they both try and break into the castle for their own reasons: brimhat trio to give King Ezrest the seed and the atelier to help save Riphilin and Beldaruit. Through this, there's great potential for Tartah and Tetia to be put in a position where they are required to utilise healing magic or medicine to help save someone. This arc can also feature Eoleo possibly being recruited by the brimhats. I would love to see an Eoleo and Custas interaction focusing on class disparity and privilege but also interactions focused on losing a parental figure.
Ultimately, an arc like this would help dismantle the balance between witches and monarchs and fully redefine said balance. King Ezrest may discover the truth of magic alongside his son, and the atelier is likely to use the window way to help rescue Riphilin and Beldaruit. Plus, if either Beldaruit or Riphilin are injured, then I can see Tetia or Tartah using healing magic or medicine to help them.