Went on a boss binge tonight and took down Dark Forge, Triomagen, Mokou, Yuyuko, and Orin.
First two were pretty easy, since they're just minor bosses. Triomagen is one of the most predictable bosses in the game, and Dark Forge is pretty tame unless it spams Cry of Anguish (which it did against me...but oh well).
Mokou I found to be a lot easier simply by not debuffing her SPD, since all of her other attacks feel weaker than Tsuki no Iwakasa's Curse anyway. I bumped up Keine's and Sakuya's FIR resistance by a ton, then just had them sit in to tank Fujiwara Volcano when it came up. The two survived easily and switched in Suwako and Youmu to finish off Mokou with their nukes.
I felt really prepared going into the Yuyuko battle, with most of my team packing complete immunity to instant death and SPI affinity of over 200. Sure enough, Saigyouji Flawless Nirvana did little to me, but this fight still went on a lot longer than I anticipated simply because Yuyuko was casting SP Drain on my main damage dealers, like Patchouli. She also kept poisoning my party, which I wasn't really as prepared for; I think I took more damage from poison than from all her other spells combined during the fight. Still, I managed to grind her out despite most of my team being poisoned or SP drained.
Orin was an interesting one. I finished off her knights with no issues at all thanks to hitting their weaknesses with Fox-Tanuki Laser, Saigyouji Flawless Nirvana, Royal Flare, and Laveatein. Orin herself did 0 damage with Cat's Walk on Keine after a buff from Minoriko, so the fight started off well. Thankfully, her boss version of Needle Hill is row-based, so Patchouli sat comfortably in the 4th slot and did heavy damage every turn with a buffed Silent Selene. Once she got low Orin started wrecking my team with Blazing Wheel, and then she silenced Minoriko with Silent Cloud, so I had to switch to all-in damage mode. Choosing to forgo switching in someone to the empty slot, I had Keine use her last turn casting Three Treasures: Sword to boost both Flandre and Shikieiki, and Starbow Break and Last Judgment combined to deal well over 100k damage to finish off Orin right there.