Cagliostro (Summer) is indispensable for Water Crit teams through her significant buffs. On top of that, she provides additional party utility through a single-target heal, Dispel, and a permanent Crit boost based on Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) stacks that is effective even from the backline. Because her kit relies heavily on Deluge Crest stacks (and in some cases, consuming them for additional effects), she works optimally with other sources of it.
How to Play
Synergy
Because Cagliostro can only provide 1 party-wide stack of Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) every 6 turns, alternate sources are needed for optimal Crit buffs.
Main Character
The Charge Attacks of Dark Opus Weapons are the most reliable source of Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) (as long as MC can C.A. often). Luckily for Cagliostro, Water's Opus weapons (/) are Staves and can be used as main weapons on Staff-proficient classes for Atma Staff synergy.
Characters
Lily (5★): After Level 90, Lily provides party-wide Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) and at Level 95, provides a party-wide reduction to Fire DMG based on Deluge Crest stacks. Her damage mitigation, party-wide healing, and debuff removal also cover Because she also has Staff proficiency, the two synergize with Atma Staff for multiattack buffs.
Macula Marius: Although Marius doesn't provide party-wide Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) , her party-wide boost to Skill DMG specs based on Deluge Crest stacks and her auto-casting skills work well with Cagliostro's Crit buffs and DMG Cap boost. Marius' heal on C.A. also supplements Cagliostro's single-target heal, and her debuffs are suited for long battles and solo content.
Maria Theresa: With sufficient enough generation of Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) , Disruption2-hit, 300% Water damage to a foe (Damage cap: ~315,000 per hit~630,000 total) and remove 1 buff. (When Cagliostro's Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) is 3 or more: Consume 1 Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) to end cooldown.) provides plenty of dispel hits which can trigger Justice ReversedWhen Sub Ally: When an ally casts a buff-removing skill: 300% Water damage to all foes (Damage cap: ~480,000). Inflict 10% ATK Down (Stackable / Max: 30%)ATK is lowered (Stackable) Strength: 10% (Max: 30%)Base Accuracy: 90%Duration: 180 seconds and 10% DEF Down (Stackable / Max: 30%)DEF is lowered (Stackable) Strength: 10% (Max: 30%)Base Accuracy: 90%Duration: 180 seconds. At level 95: Damage increased to 500%. Damage cap increased to ~720,000. Also inflict 10% Debuff Res. Down (Stackable / Max: 30%)Debuff resistance is lowered (Stackable) Strength: 10% (Max: 30%)Base Accuracy: 90%Duration: 180 seconds. At level 110: Skill upgrades to: When Sub Ally: Amplifies Water allies' skill damage by 10%. When an ally casts a buff-removing skill: 1000% Water damage to all foes (Damage cap: ~1,160,000). Inflict 10% ATK Down (Stackable / Max: 30%)ATK is lowered (Stackable) Strength: 10% (Max: 30%)Base Accuracy: 90%Duration: 180 seconds, 10% DEF Down (Stackable / Max: 30%)DEF is lowered (Stackable) Strength: 10% (Max: 30%)Base Accuracy: 90%Duration: 180 seconds, and 10% Debuff Res. Down (Stackable / Max: 30%)Debuff resistance is lowered (Stackable) Strength: 10% (Max: 30%)Base Accuracy: 90%Duration: 180 seconds. All Water allies gain Supp. DMG (Stackable / Max: 30,000)DMG dealt is supplemented (Stackable) Strength: 10,000 (Max: 30,000)Duration: Indefinite. (When a foe doesn't have removable buffs: Hit number doubles.) several times for multiple skill damage hits and allowing her to inflict maxiumum 10% ATK Down (Stackable)ATK is lowered (Stackable) Strength: 10% and 10% DEF Down (Stackable)DEF is lowered (Stackable) Strength: 10% very easily.
Summons
Princess Long Ji: Another source of Deluge CrestWater magic is amplified (Max: 5 / Can't be removed) , she also has a sub-aura that boosts Water Elemental ATK based on Deluge Crest stacks, making Crest-based teams even more powerful.
Take all the critical nodes, support skill for chance of getting crest when attacking, then Skill DMG Cap to improve her damage on her third skill. Afterwards, your selections would be Double Attack to improve her multiattack rate, or improving her survivability for longer battles with DEF nodes.