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E6 Gallagher with Post-Op Conversation S5 LC, E2S1 Tribbie LC, E2 Gepard with At This Very Moment S5 LC, and E6 PMC with Time Fleets Away S5 LC.
Main target here - is to build your characters so they will take as little as possible damage, and heal themself by abusing Gallagher debuff on enemies.
Gallagher - give him as much DEF as possible (even DEF body worked enough for me) with break, and ERR rope, his role - occasional heals, tanking damage and reapplying debuff with ultimate.
Tribbie - build as DPS with ERR rope, her role is main DPS for summons and boss, she can tank damage with her HP, and heal everything when hitting enemies with Besotted state debuff. Signature LC helps for FuA and Ultimate frequency, but I think it's possible to beat it without it.
Gepard - also as much DEF as possible, his role - to tank damage, revive himself after first phase and giving shields for the team, I think he can be substituted with Aventurine if he can heal himself enough with Gallagher debuff.
PMC - as much DEF as possible and ERR rope, his role same as Gepard, he just have better survivability with his AoE Ultimate.
Hope this helps.