Oh, I'm going to have a field day with this one.
A jester girl, who heavily changes in personality depending on the mask she wears (comedy, tragedy, wrath, shock, fear etc.). She woulf use spell cards based on clown tricks, like huge poker cards spinning across the screen or juggling fire balls and throwing them at the player. Probably low stage, but she'll reappear in later stages to throw another nasty trick at you.
A genie girl, who corrupts everyone's wishes just because she can. She would wear those typical harem clothing with lots of jewelry, and her hair looks like colorful smoke. All her spellcards revolve around wishes, and most of them have a special gimmick. For example: 'Wish for Wealth [Grave Fortune]' will make coins start raining down the screen, with sometimes gems appearing that explode into many bullets. Another idea is 'Wish for Power [Unachievable Might]', where the genie transforms in an Ex version of the main character and uses powered up versions of their spellcards. This would be a great stage 6 boss and incident starter, having corrupted everyone's wishes. It could support the pharaoh character too: the pharaoh is searching for her heirloom (the bottle where the genie resides in), and finds the player holding the bottle (the player locked the genie back in the bottle after defeating her). The player thinks the pharaoh was too irresponsible to leave such a dangerous artifact around, and fights the pharaoh to teach her a lesson. The pharaoh is the Ex Boss.
A hydra girl, or in fact girls. Nine individual girls with differing personalities bound together by a snakelike ribbon. You face the individual ones throughout multiple stages as mid-bosses, and when yo defeat them they get pulled away by the ribbon. You'll face all of them at once in stage 5 or Ex. For their last spellcard they get nine individual small life bars, and you need to deplete them one by one.
An armored girl. I already suggested a living armor loli in the Touhou 13 thread before, and I still like the idea. Very dutiful, but may be rather clumsy, like her helmet visor constantly falling shut in front of her face, obscuring her view. Her spellcards revolve around various medieval weaponry. Might be a good stage 6 mid-boss. Think of it like the Final Armor from Castlevania, which you always face before Dracula rears his head.
A girl with a heavy European theme around her, like a typical French or Dutch girl. In fact, any culture might do, as long as it's different from the standard Eastern fare.
A veeeeery sleepy Elder One girl. First appears as stage 1 boss, where she's firing danmaku in her sleep. She reappears as the stage Ex boss, now fully awake. As fitting for an Elder God, you cannot comprehend what she talking about. Not because she's so much more superior than you or speaking in a different language, but because she's a complete cloud cuckoolander and only blurts out random gibberish. She'll also have a squid hat.
Two small girls that can fuse together into a mature woman.
Zeus. That is all.
