Did the 3 trials with just Rain (6* MAX 7200HP) Laswell (Lvl 86, ~530 ATK) and Fina (5*, 3100HP). Minimalist because I don't want to invest in the story units too much.

Rain trial: Chirijaden + DW = Laswell 3TK this shit by himself. Start off with his AoE that hits 4 times, then use his 19mp skill. Rain Undermines, then provokes. Fina Cheer, then switches to Cura or Curaga depending on the party's needs.

Fina trial - 4TK, forgot to bring Sun Barette (equipped Excalibur though). Rain starts off with Undermine, Provoke, Fina with Cheer, Laswell spams 19mp skill. May possibly be prone to bad RNG, Laswell survived with 74HP after the demon's third turn.

Laswell trial = 5TK. It's slightly harder and I used an elixir to keep Rain alive, but I'll come back for the summon ticket in half a year or so :p

1st turn - Rain Undermine, Laswell 19mp skill, Fina Cheer
2nd turn - Rain Provoke, Laswell Fingersnap, Fina Cura(ga?)
3rd turn - Rain Undermine, Laswell 19mp skill, Fina Elixir on Rain.
4th turn - Rain Undermine again, Laswell Fingersnap, Fina Cheer.
5th Turn - Fina dispel, Rain Undermine, Laswell 19mp skill.

Rain should counter a lot with his own sword, so you migt finish sooner with a bit of luck.