Unmarked spoilers below.
- In keeping with Kasen's present-day Cover Identity Anomaly, she doesn't participate in most of the hermit training during the Good-Times Montage and spends a lot of it focused on the books about barriers. Of course she doesn't have a very good grasp of what hermits should be like, she barely listened during the period in which she could have learned.
- Yoshika is shown to be able to knock Kasen and Kume out of the air by tackling them and is able to tie the former to a tree despite oni being pretty strong. Even before Yoshika became a jiang shi, she had the strength of her present-day Dumb Muscle status.
- Seiga's Humans Are Bastards view. As hermits in the Touhou universe are considered different from humans, Seiga can be free to talk about how much she thinks humans suck without insulting herself.
- The reikon's rejection of Yoshika isn't a dick move like it seems. As Yoshika's speech from the third episode shows, she changed the reasoning behind her goal to become a hermit from a fear of death to wanting to do something nice for Kasen. Problem is, by choosing to go their separate ways for Yoshika to continue her quest to become a hermit, it greatly decreased the chances they would see each other again, and it took 1,200 years of unfortunate circumstances for their reunion to finally happen. The reikon wanted Yoshika to realize what she finally does at the end of the series: Spending time with Kasen rather than gaining immortality is what was important all along. Of course, he probably intended for Yoshika to just return to Kasen right after her rejection instead of asking Seiga, so he became an Unwitting Instigator of Doom by mistake.
- Of course Kasen would help the oni bandits with kidnapping humans, they might have ended up kidnapping her mother for their potential reunion!
- The later half of the story is a very tragic case of Poor Communication Kills. If Yoshika had told Kasen about her Soap Opera Disease, then maybe she would have given her the Ibaraki Box of a Hundred Medicines to cure her sickness and she wouldn't have needed to ask Seiga for help. The way things played out, Kasen was completely unaware that Yoshika was in need of help and Yoshika was unaware that Kasen had a solution to her problems.
- That bad weather during the flashback scenes with Suika and pre-oni Kasen? That's the same weather that made the villagers want to sacrifice Kasen and then settle with sacrificing her mother.
- Given how Kasen's father is never mentioned, it brings up the possibilities that either he died before the events of the story or he was among the villagers who sacrificed Kasen's mother to the water god.
- We are told that Seiga and Kan Kaku reunited, but since we don't see the latter during any non-flashback scenes, it brings up the question of why he is absent... Conflicting worldviews perhaps? Or Seiga's worldview is perhaps a result of their separation?
- The reveal that Suika was watching both Kasen and Yoshika the entire time means that Suika sat by and watched as Seiga murdered Yoshika.
- Kasen knows that the Ibaraki Box of a Hundred Medicines turns humans into oni because Suika told her, and Ascended Fridge Horror says that Suika knows because she herself was turned into an oni with it. How far back does this cycle go?
- Yoshika's ghost can reunite with Kasen at the Sanzu River, but the fact that Kasen's mother could potentially do the same is never brought up. Did being sacrificed erase her soul or something?
- She has been dead for thousands of years at that point so its entirely likely she has been reincarnated by then, or already been sorted into a proper afterlife, likely heaven do to her kindness and willingness to die for her daughters safety, coincidentally mortals CAN get into heaven before death by becoming a celestial, which is the next stage after becoming a hermit
