Guide
How the kit works
Before a fight, use Day So Right, Life So Fine! for a team heal and a 20% Max HP increase lasting two turns. In battle, Love Over the Rainbow summons Little Ica and heals the team. Each summon restores 15 Energy to Hyacine, with another 30 on the first summon through Soar, Unto the Sunlight.
Use We Who Fly Into Twilight to summon Little Ica, heal and enter After Rain. The state lasts three turns, with its duration dropping at the start of each of Hyacine's turns. While it is active, allies gain 30% Max HP plus 600. Little Ica then gets an extra turn and automatically uses Rainclouds, Time to Go! after Hyacine uses an ability.
Take Sky in Hand lets Little Ica react when an ally loses HP: at the start of a target's turn or after a target acts, Little Ica spends 4% of its own Max HP to heal that ally. During After Rain, this healing also restores HP to all allies. Little Ica has 0 SPD and does not appear in the Action Order.
Rainclouds, Time to Go! deals Wind DMG equal to 20% of the healing Hyacine and Little Ica have tallied in the battle, then clears 50% of that tally. First Light Heals the World increases Little Ica's DMG when either of them heals, stacking up to three times. Use When Breeze Kisses Cirrus for single-target damage when you do not need the Skill's healing.
Build and why
Sacerdos' Relived Ordeal and Messenger Traversing Hackerspace are other SPD set options. For planars, consider Amphoreus, The Eternal Land for team SPD while Little Ica is on the field, or Broken Keel for team CRIT DMG once Hyacine reaches 30% Effect RES.
Choose Outgoing Healing Boost on the body, SPD on the feet and HP Percentage on the sphere. Use Energy Regeneration Rate or HP Percentage on the rope. For substats, the game recommends HP Percentage first, then SPD, Effect RES and CRIT DMG. Tempestuous Halt rewards SPD above 200 with more Max HP and Outgoing Healing; Gloomy Grin already gives Hyacine and Little Ica 100% CRIT Rate.
Long May Rainbows Adorn the Sky is the first weapon choice. It gives 18% SPD and uses consumed ally HP to add damage after Little Ica's next attack. Memory's Curtain Never Falls gives SPD and a team DMG increase after Skill. The Story's Next Page is a four-star option with Max HP and an Outgoing Healing increase after the memosprite attacks.
Leveling priority
Follow the game's order: We Who Fly Into Twilight, Take Sky in Hand, Love Over the Rainbow, When Breeze Kisses Cirrus, First Light Heals the World, then Rainclouds, Time to Go! The Ultimate's healing and Max HP increase make it a useful first investment. Take Sky in Hand comes next for Little Ica's healing.
For ascension, gather 308,000 Credit, 65 A Glass of the Besotted Era and 15 each of Fear-Stomped Flesh, Courage-Torn Chest and Glory-Aspersed Torso.
To raise all skills, gather another 3,000,000 Credit, 8 Tracks of Destiny, 18 Bīja of Consciousness, 69 Seedling of Manas, 139 Flower of Ālaya, 12 Lost Echo of the Shared Wish, 41 Fear-Stomped Flesh, 56 Courage-Torn Chest and 58 Glory-Aspersed Torso.
Eidolons worth it
Cradle the Candle of Night is a good early upgrade to consider. During After Rain it adds 50% Max HP for allies, and their attacks immediately restore HP equal to 8% of Hyacine's Max HP.
O Sky, Heed My Plea is a later option: Little Ica clears only 12% of the healing tally when using its Memosprite Skill, and allies gain 20% All-Type RES PEN while it is on the field. Come Sit in My Courtyard is another option, giving an ally 30% SPD for two turns when their HP decreases.
You can leave E3 and E5 for later if you prefer new effects over skill-level increases. E4 is worth considering for a build above 200 SPD, since it adds CRIT DMG for Hyacine and Little Ica based on excess SPD.
Teams
Hyacine's kit has no stated requirement for allies of a particular combat type. Choose the team's damage dealer for the encounter, then add a buffer or debuffer. Hyacine supplies healing, a Max HP increase during After Rain and debuff removal after unlocking Stormy Caress.
One team to try is Hyacine with Castorice, Tribbie and Pela. Castorice is a Quantum Remembrance character with a memosprite, Tribbie is a Quantum buffer and Pela is an Ice debuffer. Blade is another teammate named in the guides if you want a Wind damage dealer alongside Hyacine.
Common mistakes
Do not forget that After Rain loses duration at the start of Hyacine's turns. Watch the state if you want its Max HP increase and Little Ica's automatic attacks to stay available. Little Ica's Continuous Effects also lose a turn of duration after it uses an ability.
Do not build only for SPD and neglect HP Percentage: Max HP determines much of Hyacine's healing and Little Ica's initial Max HP. Avoid treating Rainclouds, Time to Go! as damage from the whole healing tally after every use, since each use clears half of it before E6.