Characters I don't know about:

- The ghost face on Jo'on's pile of money (multiple people identified it as a kedama)

- The two in the sailor uniform (unless one of them is Chiyuri?)
 (artist confirmed on Twitter they're Feza and Nua Kouzui, original characters from the Touhou fangame Wonderful Waking World)
- The pink mermaid (artist confirmed on Twitter it's Iroha Tsubasa, an original character from the Touhou fangame Sapphire Panlogism)
- Whatever that is on Seiga's needle (actually not a character, but a spell card reference — I asked the artist and the response was "One of her spellcards is her throwing electrified looking fetuses at you. you can't tell in-game but its by the name of the spellcard and the chinese thing its related to"; cross-referencing with touhouwiki it'd most likely be one of "Evil Sign "Yang Xiaogui"", "Path Sign "Dao Fetal Movement"", or "Path Sign "TAO Fetal Movement ~Dao~"")

andlabs said:

Characters I don't know about:

- The ghost face on Jo'on's pile of money

Looks like a kedama