Castorice represents a paradigm shift in Honkai: Star Rail’s combat design. As a Quantum-type character following the Path of Remembrance, she eschews the traditional Energy system entirely, opting instead for a high-risk, high-reward HP-consumption mechanic. Building her effectively requires a departure from standard DPS templates, focusing heavily on Max HP, Crit optimization, and specialized team synergies that can handle her relentless drain on party resources.

Core Mechanics: The New Bud and Netherwing System

To understand a proper Castorice build, one must first master the "New Bud" system. Unlike other characters who generate Energy through actions or being hit, Castorice accumulates New Bud points whenever any ally loses HP. This includes damage taken from enemies and, more importantly, the self-inflicted HP drain from her own skills.

Once the New Bud meter reaches its limit, she can unleash her Ultimate, "Doom Shriek, Dawn's Chime." This action summons her Memo Sprite, Netherwing (specifically Pollux), to the field and deploys the "Lost Netherland" territory. This territory is a massive asset, as it decreases all enemies' All-Type RES by a significant margin. The Netherwing functions as a separate entity on the action bar with a base Speed of 165, acting as a backup unit that inherits Castorice’s damage buffs. While Netherwing is active, it protects the team by absorbing damage that would otherwise down an ally, provided the team can keep up with the HP conversion.

Trace Priority and Ability Breakdown

The hierarchy of Trace leveling for Castorice centers on maximizing the scaling from her Max HP. Since almost every part of her kit, from her Basic ATK to her Memo Sprite’s follow-up instances, scales with HP, neglecting her survivability nodes is not an option.

  1. Ultimate / Talent: These should be prioritized equally. The Ultimate dictates the strength of the Netherwing and the RES PEN of the territory, while the Talent governs the damage multiplier gained from HP loss stacks.
  2. Skill: The Skill is your primary method of force-feeding New Bud points. It consumes a percentage of the entire team's current HP to deal Blast-type Quantum damage.
  3. Basic ATK: While secondary, it still scales with HP and serves as a filler when managing specific HP thresholds.

Key Bonus Traces to unlock early include Contained Dark Tide, which allows incoming healing to be converted into New Bud points (or Netherwing HP), ensuring that a high-output healer like Gallagher or Hyacine contributes directly to her offensive uptime.

Best Light Cones for Castorice

Castorice’s Light Cone options are relatively narrow due to her unique HP-scaling nature within the Remembrance Path. Most existing Remembrance cones focus on Freeze or Effect Hit Rate, which are of little use to her pure DPS kit.

Top Tier: Make Farewells More Beautiful

This is her signature 5-star Light Cone and is considered a massive power spike. It provides a substantial boost to Max HP and allows both Castorice and her Memo Sprite to ignore a portion of the enemy’s DEF. Given the rarity of DEF ignore in other parts of her kit, this cone significantly raises her damage ceiling in endgame content.

Competitive Alternative: To Evernight's Stars

While primarily designed for other Remembrance units, the HP boost and the team-wide DEF ignore for Memo Sprites make this a strong second choice. It helps stabilize the Netherwing’s damage output, even if the energy-related passive is wasted on Castorice.

Free-to-Play and 4-Star Options

For players without 5-star options, The Flower Remembers or Sweat Now, Cry Less (often found in Battle Pass or event rewards) are viable. If these are unavailable, look for any Light Cone that offers raw HP stats. Because her damage scales so aggressively with HP, a high-stat 5-star cone from a different path might sometimes outperform a lower-stat Remembrance cone, though the passive will be inactive.

Relic Sets and Optimal Substats

The relic selection for Castorice is perhaps the most counter-intuitive part of her build, particularly regarding the Speed stat.

Cavern Relics: Poet of Mourning Collapse (4-Piece)

This set was tailor-made for the Quantum Remembrance playstyle. The 4-piece bonus increases Crit Rate significantly, but only if the wearer’s Speed remains low. This creates a specific build path where HP% Feet are vastly superior to Speed Feet. By staying slow, Castorice ensures she maintains the full Crit Rate buff from the Poet set, while her Netherwing (which has its own high base Speed) handles the frequent turn rotations.

Planar Ornaments: Bone Collection’s Serene Demesne

This ornament set provides another layer of HP scaling and Crit Damage. It is widely considered her best-in-slot because it rewards the high HP pools that Castorice naturally reaches. An alternative for those struggling with Crit Rate is The Wondrous Banana Amusement Park, though it offers less overall synergy with her Memo Sprite mechanics.

Recommended Stat Benchmarks

  • HP: 7,000+
  • Crit Rate: Aim for 80% (which should reach 100% in-combat with the Poet set and buffs).
  • Crit Damage: 150%+
  • Speed: Keep at base or very low to maintain Poet set stacks.

Piece Main Stats

  • Body: Crit Damage
  • Feet: HP%
  • Sphere: Quantum Damage or HP% (depending on which has better substats; they are often comparable due to her high internal damage buffs).
  • Rope: HP%

Team Compositions and Synergy

Castorice requires a team that can survive her HP drain while contributing to the New Bud tally. Shielders are generally a poor fit because they prevent the "HP loss" required for her mechanics. High-output healers are mandatory.

The Premium Team: The "Endless Cycle" Comp

  • DPS: Castorice
  • Support: Evernight
  • Support: Cyrene
  • Sustain: Hyacine

In this setup, Hyacine is the linchpin. She increases the team's Max HP and consumes HP to heal, which accelerates Castorice’s Ultimate generation. Evernight and Cyrene provide offensive buffs that specifically target the scaling of Quantum and HP-based units.

The Dual DPS HP-Consume Team

  • DPS: Castorice
  • DPS: Blade or Jingliu
  • Support: Tribbie or Ruan Mei
  • Sustain: Gallagher

Blade is an excellent partner for Castorice. His self-harming mechanics count toward her New Bud points, and she, in turn, helps him reach his follow-up attack triggers faster by draining his HP with her Skill. Gallagher serves as the sustain here because his "Besotted" debuff allows allies to heal themselves by attacking, which Castorice’s frequent instances of damage can trigger constantly.

Free-to-Play Friendly Team

  • DPS: Castorice
  • Support: Remembrance Trailblazer (Ice)
  • Support: Pela
  • Sustain: Lynx

Lynx is the MVP for budget builds. Her Skill increases the Max HP of the target (Castorice) and provides a continuous heal that mitigates the drain from Castorice’s skill. Pela provides the much-needed DEF shred to amplify the Quantum damage.

Eidolon Analysis: Is She Worth Pulling Duplicates?

Castorice is highly functional at E0, but her eidolons offer substantial quality-of-life and damage improvements.

  • E1 (Snowbound Maiden, Memory to Tomb): Increases damage dealt based on the enemy’s remaining HP. This makes her an exceptional finisher in boss fights.
  • E2 (Crown on Wings of Bloom): This is a major stopping point for many players. It improves the Netherwing's action advance and scaling, making the rotation much smoother and less reliant on external turn manipulators.
  • E4 (Sunlight's Reflection on Ice): Provides a team-wide HP boost and improves the survivability of the Memo Sprite.
  • E6 (Wait for Years to Loom): The ultimate upgrade. It allows her to ignore enemy Weakness types and provides massive Quantum RES PEN, effectively allowing her to brute-force any content in the game regardless of elemental resistance.

Advanced Gameplay Strategy

Playing Castorice effectively requires a shift in mindset. You are not just managing Skill Points; you are managing the collective health bar of your party.

Managing the "Moon Cocoon" State: Castorice’s unique global passive allows allies who take a killing blow to enter the "Moon Cocoon" state. They don't die immediately but delay their downed state until after their next action. If they are healed during this window, they are saved. This allows you to play much more aggressively with her HP-draining Skill than you would with other characters. You can intentionally drop an ally to 1 HP to cap out your New Bud meter, knowing that the Moon Cocoon will protect them for one more turn.

Speed Tuning with Netherwing: Because Netherwing’s actions are independent of Castorice’s Speed, you should focus on making your supports fast. If your supports (like the Remembrance Trailblazer or Sparkle) act frequently, they can generate Skill Points and trigger healing, which in turn fuels Castorice’s next summon. Castorice herself should remain the "anchor" of the team—slow, heavy-hitting, and high-HP.

In summary, the best Castorice build is one that embraces her unique niche as an HP-scaling juggernaut. By prioritizing Max HP over Speed and pairing her with healers who can turn her risks into rewards, you can unlock a level of damage that few other Quantum units can match. Whether you are tackling the latest Memory of Chaos or exploring the deeper layers of the Simulated Universe, a well-built Castorice is a harbinger of victory.