After several attempts, I finally beat Ran (with 2 events triggered, 1 of which is mandatory.)
This battle is seriously one of the most frustrating boss fight ever. I have to maxed out some of the characters' spells to make the status effect land consistently, like Maribel's Chaotic for SHK and Mystia for SIL.
My front liners were Byakuren, Satori, Suwako and Patchouli. The battle started with Ran summoned her shikigamis and she was so freaking fast that she reached 7000 ATB before I could get a turn. Suwako went first and I used her to lower Ran's and her shikigamis'' Mind with her CLD move, which Ran was weak to. Then, Byakuren went second and I used her to switch Suwako in for Mystia to instantly inflict the shikigamis' with Silence. If Byakuren had a spare turn, I would have her spamming Magic Milky Way to cripple the enemies. If she was heavily injured, I would switch her out for Ran for buffing. Patchouli alternated between concentrating and firing off her Princess Undine, which could one-shot those shikigamis with both Mind debuff from Suwako and Silence from Mystia, dealing 20k each. Satori was just there, waiting for the right opportunity for an important person to be switched in. Other than that, Ran's spells are pretty straightforward (except for Destroy Magic) but with her limited movesets, she could spam them indefinitely. Even then, with her shikigamis present, Ran's spells were quite deadly even without buffs, capable of one-shotting any fragile characters,
After firing off the first Princess Undine, I switched in Mystia for Maribel, Satori and Maribel then kept casting Chaotic spell to lock Ran down with a Shock effect. Luckily, it landed consistently, buying Patchouli enough time to concentrate and fire 2 more Princess Undine. Then Ran suddenly turned serious, firing off her Soaring En no Onzuno, killing Satori and Maribel. So, I switched in Yuugi, Marisa and Utsuho to blast everything until Ran died. Patchouli then ended the battle with the last Princess Undine.
It took about 10 retries before I finally won the battle, somehow.
So, I was able to take Ran down with only 2 events triggered but I wonder if it is possible to beat Ran with only 1 event triggered.