I fought super Tenshi on F6 and no matter how hard I tried, I couldn't get her. On my final try before I just gave up and let her run away, I could only get her down to 50% HP by having Wriggle poison her over and over, and that was like my best run of all my attempts. The team was around level 30, with Komachi getting a lot of investment in HP in the magic library so she could survive the first hit from Tenshi (Komachi had 3000+ HP and like 180 MYS resistance to accomplish this) and I basically ran the strat on the wiki, Aya getting two turns before Tenshi's first move to cast haste on Wriggle and Satori, who then spam Comet on Earth at Tenshi and pray it triggers the poison effect. At this point things had to go perfect, Tenshi had to take the first attack to hit Komachi, and then Komachi couldn't die - this was still not a guaranteed thing, if Tenshi rolled high on her damage she could still one-shot Komachi. Komachi uses Narrow Confines and I pray it debuffs the heck out of Tenshi. From that point on things get more crazy, somebody dies every turn so I didn't even bother healing Komachi or anyone else and just prayed it wasn't Wriggle. On that last run Wriggle made it until Tenshi ran away and I still couldn't get her. I guess my advice to others is grind to far higher than level 30 if you absolutely have to win the fight, but you can get almost everything she drops (just not the Divine Barrier/Treasure Chest Key, I think) if you let her go.
(EDIT) Misc notes on my setup: Aya had two levels in that skill that gives her 20,000 ATB to start the fight to guarantee she'd have it and the skill that makes her speed everyone else up on her turn, Wriggle had Toxicologist and invested in the subclass skill that makes Poison skills hit harder when they connect. Satori just had levels in the skill that lets use other characters' spellcards. Komachi had +HP maxed out, and a few levels in Narrow Confines. My plan after that first turn initially was to bring in Hina and nail Tenshi with her huge debuff move, but more often then not that hurt my team too much with the debuffs since Hina was generally only going to live for a turn anyways. I think there could be something there though, because a full debuffed Hina can hit Pain Flow for upwards of 8000 damage, which might be a way to finish Tenshi off. Master Spark only hit for like 5k, unfortunately.