'll give you the full details!
The only compound technique in the game right now is Zandion (Lighting/Wind). It DOES gain additional damage from the Lighting Masteries (Fo) and Wind Masteries (Te). It cannot be "equipped" to a weapon and can only be placed on the subpalette. It charges up similiar to a photon blast, but it only charges when you're using techniques. It has a base damage of 2500% and counts as a normal tech, so the higher your t-atk the more damage it will do. Just like a PB it resets when you go back to the campship.
You can get the quest for it when you're on the episode 3 matterboard and your MAIN class (not your sub) is a level 70+ Force or Techer. The quest comes from Claris Claes who'll appear not too far from where Klotho is standing.
The client order itself is to kill 70 enemies on Ultimate using techniques only. This basically means you have to get the "kill hit" with a technique, so even if you damage the enemy with techs if someone else gets the kill it won't count. It can be quite grindy to do if you haven't got a good MPA or the MPA is too well geared and you can't get the last hit in. If you're a melee Techer it can be a pain in the butt (though you can melee the enemies and then finish them with a tech if you watch your damage), Forces should have no issues getting it after about 3 runs.
Hope that helps! It's a fun technique and I'm curious to see what other ones they'll come up with in the future! It's also manly as hell so I hope you like being