S-tier PvE reasoning
Charlotte applies poison, airborne, and knockdown — three ailment types for Signal Skill fuel. Theresia's flail reach clears mob packs while applying bleed and stun. Dana (with summon Chako) draws aggro and adds frost pressure for safe boss learning. Johnny's Phantom Slash sets airborne juggles that delete boss HP bars when the gauge breaks.
A-tier story workhorses
Lute is the campaign protagonist — balanced, always available, and tuned for tutorial pacing. Castella's axe spin continues off-field when you swap, enabling solo combo setups. Renia (Raina) is a premier air-juggle initiator with Rising Cutter and Wind Slayer. Roxy brings bleed ranged DPS for enemies that kite melee. Logan anchors as a Warrior initiator with high HP and execution-style burst.
B-tier — invest after core
Kalien's burn fox summons are straightforward but want teammates who detonate burn efficiently. Veronica fits burst DPS slots once gear catches up. Eileene and Alex are honest melee fighters — great if you enjoy halberd or sword-and-board, less meta than ailment stackers. Tarte offers shock damage but slower orb animations.