Touhou Puppet Dance Performance: Shard of Dreams - Neo Puppet Liberation Front Seija
First things first, I had to reupload this stupid video because OBS stopped working right and didn't record audio, and it took me a while to notice, so that's real fucking good. You'll unfortunately have to deal with some music added via the magic of shitty video editing, because there's nothing else I can do.
Seija's the third big required postgame boss after Flandre and Medicine, and can be kind of a pain if you didn't do any of the sidequests before fighting her.
Assist Tewi (Void) lives to set traps like the Bind Trap (lowers Speed on switch) and Stealth Trap (does Steel type damage on switch). She even has a Black Choker to almost always guarantee she gets a trap up, but if you have a move like Smash Spin (which you should, it's a Skill Card) you can get rid of the hazards easily.
Extra Nue (Wind/Nether) does a lot of Fo. Attack damage, boosted further by her Charge! ability. She's also surprisingly tanky.
Assist Sekibanki (Dark/Nether) is just here to set the Heavy Fog weather condition, which strengthens Dark type skills and weakens Light type ones. She also holds an Almighty Godstone to make it last longer than 5 turns.
Speed Kagerou (Dark/Wind) usually uses Moon's Protection to boost her Spread stats by 1 stage, which is pretty easy for her to pull off considering a Bind Trap may be up on your side. Hit her on the Focus side and don't let her power up.
Speed Wakasagi (Water/Sound) is a glass cannon that deals high damage with Water, Sound, and Wind skills, boosted even further by her Straw Doll.
Defense Seija (Poison/Light) has huge Sp. Defense and good Fo. Attack, as well as a Jar of Poison to heal her every turn. Her favorite move is Venom Nova, a Poison type skill, so try switching in a Steel type Puppet.