Sunday has arrived as a revolutionary Harmony character in Honkai Star Rail, specifically designed to bridge the gap between traditional hypercarries and the rising "Summon" meta. As an Imaginary-type follower of the Path of Harmony, his kit is not just about general buffs; it is a precision tool for action manipulation and critical damage scaling. This guide provides a comprehensive breakdown of the optimal Sunday build, drawing from high-level data analysis and practical gameplay testing.

To maximize Sunday’s potential, players must focus on his unique ability to advance the actions of both characters and their summons (like Jing Yuan’s Lightning-Lord or Topaz’s Numby). This makes him a direct upgrade over older Harmony units in specific niche compositions.

Quick Summary for Sunday’s Best Build

For those looking for a rapid setup, here is the most effective configuration for Sunday in the current version:

  • Core Role: Support / Action Advancer / Summon Buffer.
  • Best Light Cone: A Grounded Ascent (Signature).
  • Best Relic Set: Messenger Traversing Hackerspace (4-Piece).
  • Best Planar Ornament: Broken Keel or Lushaka, the Waters of Service.
  • Main Stats: CRIT DMG Body, SPD Feet, HP/DEF Sphere, ERR Rope.
  • Stat Priorities: CRIT DMG > SPD > Effect RES > Bulk (HP/DEF).

Detailed Skill and Mechanic Analysis

Understanding Sunday’s kit is essential before diving into his gear. Unlike Bronya, who primarily focuses on the character, Sunday’s influence extends to the "entities" linked to the character.

Skill: Benison of Paper and Rites

This is the core of Sunday’s gameplay. It enables a designated ally and their summon to take action immediately. Furthermore, it increases their DMG dealt by a substantial percentage.

  • The Summon Synergy: If the target has a summon, the DMG boost is significantly higher. This is a game-changer for characters who previously struggled with "slow" summons that couldn't be sped up by conventional means.
  • Skill Point Economy: When used on a "Beatified" target (from his Ultimate), Sunday recovers 1 Skill Point, making him much more SP-efficient than Bronya in long battles.

Ultimate: Ode to Caress and Cicatrix

Sunday’s Ultimate is a massive energy and CRIT DMG battery. He regenerates 20% of the target's max energy (with a minimum floor of 40 energy due to his Major Traces) and grants the "Beatified" status.

  • CRIT DMG Scaling: The CRIT DMG buff provided to the ally is based on a percentage of Sunday’s own CRIT DMG plus a flat base value. This is why stacking CRIT DMG on Sunday is non-negotiable.
  • Duration: The buff lasts for 3 turns, decreasing at the start of Sunday’s turn. This long duration allows for high uptime even in fast-paced encounters.

Talent: The Sorrowing Body

Whenever Sunday uses his skill on an ally, he increases their CRIT Rate for 3 turns. This passive significantly lowers the relic requirements for your DPS characters, allowing them to focus more on CRIT DMG or ATK.

Optimal Relic Sets and Sub-stat Optimization

Sunday requires a delicate balance of speed and critical stats. Because his buffs scale off his own attributes, his relic quality directly impacts the team's total damage output.

Best Cavern Relics

  1. Messenger Traversing Hackerspace (4-Piece)

    • 2-Piece: Increases SPD by 6%.
    • 4-Piece: Increases the SPD of all allies when the wearer uses their Ultimate.
    • Why it works: This is the standard choice for most Harmony units. Since Sunday needs to act frequently to cycle his Skill and Ultimate, the extra SPD is invaluable. The team-wide SPD buff also helps his DPS stay ahead of enemy cycles.

  2. Eagle of Twilight Line (4-Piece)

    • 2-Piece: Increases Wind DMG (Useless for Sunday).
    • 4-Piece: After the wearer uses their Ultimate, their action is Advanced Forward by 25%.
    • The Advanced Strategy: For endgame players looking to maximize "Zero-Cycle" clears in Memory of Chaos, this set allows Sunday to act more often by manipulating his own action bar. However, it requires much stricter SPD tuning.

  3. 2-Piece Combinations (Messenger + Longevous Disciple/Guard of Wuthering Snow)

    • If you cannot reach the desired SPD or CRIT DMG thresholds with a 4-piece set, mixing sets for survival and speed is a viable mid-game strategy.

Best Planar Ornaments

  1. Broken Keel

    • Effect: Increases the wearer's Effect RES. When Effect RES is 30% or higher, all allies' CRIT DMG increases by 10%.
    • Analysis: This is arguably the best-in-slot ornament for Sunday. It synergizes with his need for CRIT DMG and provides him with the resistance needed to avoid being crowd-controlled, which would stop his buffs from ticking.

  2. Lushaka, the Waters of Service

    • Effect: Increases Energy Regeneration Rate (ERR). If the wearer is not the first character in the team lineup, increases the ATK of the first character.
    • Analysis: A great alternative if your DPS is placed in the first slot. The ERR boost helps Sunday reach his 130-cost Ultimate faster.

  3. Fleet of the Ageless

    • Effect: Increases HP. When SPD is 120 or higher, all allies' ATK increases by 8%.
    • Analysis: Use this if your team relies heavily on ATK scaling rather than CRIT DMG, or if Sunday is struggling to survive hard-hitting boss attacks.

Light Cone Hierarchy

Light Cones are the primary source of Sunday's base stats and utility. His signature cone is significantly ahead of other options, but there are strong F2P alternatives.

1. A Grounded Ascent (5-Star Signature)

This Light Cone provides everything Sunday needs:

  • High base CRIT DMG.
  • Energy regeneration when using skills.
  • A unique stackable buff that increases the team's DMG when the wearer uses their Skill or Ultimate.
  • It specifically caters to the SP recovery mechanics of his kit, making him a truly SP-positive support.

2. But the Battle Isn't Over (5-Star Standard)

Bronya’s signature cone is excellent on Sunday.

  • Increases ERR.
  • Restores a Skill Point when using an Ultimate.
  • Increases the DMG of the next ally taking action after the wearer uses their Skill.
  • Since Sunday is an action-advancer, the "Next Ally" buff is almost always guaranteed to hit your DPS.

3. Past and Future (4-Star F2P)

Available through the Forgotten Hall shop, this is the best non-gacha option.

  • It mimics the DMG buffing of "But the Battle Isn't Over" without the energy regeneration. At Superimposition 5 (S5), the DMG boost is very competitive.

4. For Tomorrow's Journey (4-Star Event)

If you participated in the previous Harmony-focused events, this cone provides a solid ATK boost and DMG increase for the wearer after using an Ultimate. While Sunday doesn't care about his own DMG, the stat stick helps with general utility.

Stats and Breakpoints: The Math Behind Sunday

To build a "Perfect" Sunday, you need to hit specific numbers to ensure his rotations are fluid.

Speed (SPD) Breakpoints

Sunday’s base speed is 96, which is relatively low for a Harmony unit.

  • 134 SPD: The baseline for Memory of Chaos. This allows Sunday to act twice in the first cycle.
  • 160+ SPD: The "Hyper-speed" build. This is ideal if your DPS is slow (running ATK boots instead of SPD boots). Sunday will "carry" the DPS by constantly pulling them forward.
  • Note on Speed Tuning: If you are running Sunday with Jing Yuan, Sunday should ideally be slightly faster than Jing Yuan to maximize the "Double Action" potential of the Lightning-Lord.

CRIT DMG Targets

Since Sunday transfers a portion of his CRIT DMG to his allies:

  • Low End: 150% CRIT DMG.
  • Ideal: 200% - 220% CRIT DMG.
  • Whale/Endgame: 250%+ CRIT DMG. Achieving these numbers requires a CRIT DMG Body piece and high-roll sub-stats on every other piece.

Energy Regeneration (ERR)

With a 130 Energy cost, Sunday needs help to maintain a 3-turn Ultimate rotation.

  • An ERR Rope is mandatory.
  • Without his signature light cone or "But the Battle Isn't Over," Sunday may occasionally need a 4-turn rotation or external energy sources like Huohuo or Tingyun.

Best Team Compositions for Sunday

Sunday shines brightest when paired with characters that have follow-up attacks or summons, but his 100% action advance makes him versatile.

1. The "Ultimate Summon" Team

  • Main DPS: Jing Yuan
  • Support 1: Sunday
  • Support 2: Robin or Tingyun
  • Sustain: Aventurine or Huohuo
  • Synergy: Sunday advances Jing Yuan, which builds stacks for the Lightning-Lord. Sunday’s buffs also specifically apply to the Lightning-Lord, solving the historic problem of the summon "falling off" buff windows.

2. The FUA (Follow-Up Attack) Duo

  • Main DPS: Topaz & Numby
  • Sub-DPS: Dr. Ratio or Feixiao
  • Support: Sunday
  • Sustain: Aventurine
  • Synergy: Sunday can choose to advance Topaz to accelerate Numby’s turns, or advance the primary carry depending on the tactical situation.

3. Traditional Hypercarry

  • Main DPS: Dan Heng Imbibitor Lunae or Argenti
  • Support 1: Sunday
  • Support 2: Sparkle or Ruan Mei
  • Sustain: Any high-tier sustain
  • Synergy: Sunday acts as a "Secondary Bronya." In teams with Dan Heng IL, his Skill Point recovery becomes vital.

How to Play Sunday: Rotation and Strategy

Managing Sunday is about timing his Ultimate to maximize the "Beatified" window.

  1. Opening: Start with Sunday's Technique to grant an immediate DMG boost to the first ally he buffs.
  2. Skill Usage: Always use Sunday’s Skill on your primary DPS. If you have an E1 Sunday, this also provides DEF shred.
  3. Ultimate Timing: Use Sunday’s Ultimate after the DPS has used their own Ultimate or at the start of a major burst phase. This ensures the CRIT DMG transfer covers the most impactful hits.
  4. SP Management: Monitor the "Beatified" status. Sunday only recovers a Skill Point if he uses his Skill on an ally who is already under the effect of his Ultimate. This creates a rhythmic "Ult -> Skill -> Skill" cycle that stays SP neutral.

Comparison: Sunday vs. Bronya vs. Sparkle

  • Sunday vs. Bronya: Sunday is more SP efficient and buffs summons. Bronya offers a higher raw DMG % buff on her Skill but lacks the CRIT Rate talent and the energy battery mechanics of Sunday.
  • Sunday vs. Sparkle: Sparkle is the queen of Skill Point generation and mono-quantum teams. Sunday is superior for teams that need 100% Action Advance (Sparkle only provides 50%) and for summon-heavy compositions.

Summary of Sunday's Build Potential

Sunday is a high-investment, high-reward character. While he can function with basic gear, he truly transforms a team when equipped with high CRIT DMG and enough Speed to dictate the flow of battle. He is the definitive support for the 2.7+ meta, especially as more summon-based characters enter the roster.

Key Takeaways

  • Prioritize CRIT DMG above all else for buff scaling.
  • 134 SPD is the minimum goal, but 160 SPD unlocks his true potential.
  • Summon teams are his home, but he is a viable side-grade to Bronya in almost any hypercarry team.
  • Signature Light Cone is a massive quality-of-life upgrade for SP management.

FAQ: Frequently Asked Questions about Sunday

What is the minimum Energy Regeneration needed for Sunday?

To maintain a consistent Ultimate every 3 turns, you need a 5-star ERR Rope and at least one other source of energy, such as his signature light cone or being hit by enemies. Without these, you will likely fall into a 4-turn rotation.

Does Sunday work with Acheron or Feixiao?

Sunday can work with them as an action advancer, but his Ultimate’s energy regeneration is wasted on Acheron (who uses Slashed Dream stacks) and Feixiao (who uses Flying Aureus). For these characters, Robin or Sparkle are generally better suited.

Should I pull for Sunday’s E1 or his Signature Light Cone?

If you are struggling with Skill Point management, the Signature Light Cone is the priority. If you want more raw damage and DEF penetration, his E1 is an incredibly strong buff that makes him competitive with top-tier E0S1 supports.

Can Sunday buff himself?

While Sunday benefits from his own stats, his Skill and Ultimate are designed to be used on other allies. Using them on himself is inefficient and generally not recommended in any serious combat scenario.

Why is 100% Action Advance better than 50%?

A 100% advance (like Sunday and Bronya) allows a DPS to act immediately regardless of where they are on the action bar. A 50% advance (like Sparkle) might not bring the DPS to the top if they are very far down, making Sunday much more reliable for "dragging" slow, high-ATK characters forward.