Guide
How the kit works
Start in Answering Form and build Answering Heart with attacks and Heartward by Moon. An Intro Skill in this form grants 60 points. At 100 points, hold Normal Attack to use the special Heavy Attack from Forms Turn, Heart Abides. It deals Electro DMG counted as Resonance Skill DMG and unlocks the form-changing cast of Nexus Alight.
Cast the unlocked Liberation to enter Illumining Form and gain Edict. After an on-field Resonator deals damage, Edict can trigger a Coordinated Attack once per second. You receive 21 stacks for 45 seconds.
In Illumining Form, build up to 300 Illumining Heart, then use Resonance Skill on the ground to enter Mechanism Dominion. Enhanced Basic Attacks consume the resource on hit. Once it reaches zero, hold Normal Attack for the special Heavy Attack, then use the Liberation finisher when Resonance Energy is full. The finisher returns Hsin to Answering Form.
In Unison mode, an Intro Skill in Answering Form makes the next form-changing Liberation grant Unison for 5 seconds. Switching with Unison triggers Hsin's Outro Skill and the incoming character's Intro Skill. An Intro in Illumining Form sends Hsin directly into Mechanism Dominion with 300 Illumining Heart.
In Electro Flare mode, team applications of Electro Rage give Hsin Heart of Thunder, up to 100 stacks. Her Resonance Skill uses those stacks to trigger Electro Flare DMG. The form-changing Liberation also lets her gain 150 Illumining Heart once by collapsing the Modular Heartlock made by her first Basic Attack in Illumining Form.
Build and why
Use five pieces of Heart of Sworn Vigil. Its listed two-piece effect gives 10% Electro DMG, which suits Hsin's attacks. The five-piece effect is not specified in the available set data. ATK and Electro DMG Bonus are worth considering: her Outro scales with ATK, and her kit deals Electro DMG.
Blooming Jadehaven is the first weapon choice. After Hsin inflicts Electro Flare or triggers Unison Response, it amplifies Resonance Skill DMG by 36% and ignores 10% of the target's Electro RES. It also amplifies nearby targets' Electro Flare DMG while she is active.
Lethean Elegy is the next option: after Echo Skill DMG, it grants Resonance Skill DMG Bonus and lets damage ignore some DEF. Stringmaster follows, with Attribute DMG Bonus and ATK gained from dealing Resonance Skill DMG. Cosmic Ripples and Augment are alternatives; the former provides Energy Regen, while the latter grants ATK after Resonance Liberation.
Leveling priority
A suggested order is Forms Turn, Heart Abides, then Nexus Alight. The Forte covers the special Heavy Attacks and mode mechanics, while the Liberation includes the finisher and Coordinated Attacks.
Next, consider Heartward by Moon, followed by Glance on a Whim and Manifold Bloom. The Skill is used in both forms, and the enhanced Intro matters in Unison teams. This is a suggested order rather than a game-provided priority.
For ascension, collect Shell Credit, LF Autopuppet Kernel, MF Autopuppet Kernel, HF Autopuppet Kernel, FF Autopuppet Kernel, Solidarity's Loneflame and Bloom of Hearkening. Skill upgrades also use those four Kernel materials and Shell Credit, plus Remnant of the Wheel, Spliced String, Broken String, Solidified String and Melodic String.
Resonance Chain nodes worth it
For a large damage upgrade, consider The Moon Owes Its Light to the Living (sequence 6) first. It makes targets take 40% more Resonance Skill DMG from Hsin and lets that damage ignore 20% DEF. In Electro Flare mode, nearby targets' Electro Flare DMG can also critically hit.
A Dream of Return Among the Hills (sequence 3) is another option for the Liberation finisher: it increases its DMG Multiplier by 70% and adds a mode-specific effect. To Wake Is to Wonder What I Am (sequence 2) increases the special Heavy Attack multipliers and restores 100 Answering Heart on entering combat, subject to its cooldown.
These are suggestions, not required stopping points. A River of Lanterns, a River of Wishes (sequence 4) gives the team All-Attribute DMG Bonus under its listed conditions, while Forms Turn as the Heart Wills (sequence 5) offers damage reduction and protection from a fatal blow. You can stop before these if those benefits are less useful to you.
Teams
Rover: Electro is a named partner with a direct connection to Tides of Succession. In Electro Flare mode, when Rover: Electro casts the listed Intro Skill, both characters gain 20% Electro DMG Bonus for 30 seconds. Teammates who inflict Electro Rage also help Hsin build Heart of Thunder.
Shorekeeper and Buling are other teammate options named by guides. A sustain slot is worth considering: Hsin's Moon Fox healing works out of combat, not as a replacement for in-combat healing.
Common mistakes
Don't hold the special Heavy Attack in Answering Form before filling Answering Heart, or expect the Illumining Form finisher before consuming Illumining Heart and using its special Heavy Attack. The final Liberation also needs full Resonance Energy.
Don't switch out too early during the Electro Flare Resonance Skill: ending it early removes its listed Electro Flare effect. In Unison mode, watch the 5-second Unison window after the form-changing Liberation if you want the switch to trigger both skills.
Don't assume Moon Fox heals during combat. It also disables Resonance Liberation while active, so leave the form before trying to use it. Keep some STA for the special Heavy Attacks rather than spending it all on movement or aerial attacks.