Setup Explaination (Gear shown at the end of the video)
Taion - As the character with the highest base tp out of the whole cast, his role is to reach for the bravo rating on round 1 and amazings on all future chain attack rounds. Aerial Slash is incursor's highest damage art and fused with Hidden Thorn. This is a powerful bleed and actually gets its damage cap increased depending on certain gear setups. Glitter Stream, Shield Bash, Soaring Tempest are standard combo reactions and Mystic Vision is a Crit damage increase although wasn't used. Its important to note, Taion has Swelling Scourge X gem and a Rage Amulet accessory. Both of those increases the strength of bleed and is what increases the damage cap for the bleed tick.
Noah/Eunie - Noah and Eunie have the next highest base TP which lets Taion reach Amazing on round 2 without using more additional characters than necessary. They're built for support Soulhacker primarily focusing on increased buff strength. Desperate Chage + Battle Pheromone are incredibly powerful Crit Buffs and can be maintained throughout the Chain Attack. The only major difference between this Soulhacker Build and the others is one of the skills increases buff strength instead of increasing damage. Dragon's decree is fused with Draining Vacuum so that they can pass power charge while still doing damage. They have a gem to increase HP on revival because setting this up with 15+ mobs in combat is difficult and this helps making sure everyone is alive when the chain attack starts.
Mio/Lanz - Damage Soulhackers. This time buffing isn't the main focus so the Gem mentioned earlier is replaced with Attack Up. Transient bond is fused with Draining Vacuum this time for the most damage. Even though Wild Wave + Elimination Beam is the strongest fusion, I don't use them because they're forward AOE attacking arts which ruins the whole setup of keeping a pack of mobs alive.
Sena - AOE Nuker. This build is very similar to Mio and Lanz's setup but replaced one of the skills for a skill that increases the range of AOE attack arts. Sena still has Draining Vacuum and Transient Bond for the second to last round of damage. She has Psychowave, an AOE art around the user and does increased damage to Keves enemies (which we so happen to be against). This is fused with Elimination Beam for high damage.
Fiona - Not much to say here since you can only adjust what arts are used and the accessories. Analyzer Scope increases base TP by 10 which was important to reach Amazing on round 2. The other accessories are for increasing damage for when Fiona does her Order finisher.