The best Sparkle build in Honkai: Star Rail centres around buffing her crit damage so she can provide an even more potent crit damage boost with her skill. Sparkle is really just an enabler for damage-dealers who eat through your skill points, since she grants two extra points for the team, and can recover four through her ultimate. 

Add to this her skill that buffs team-wide crit damage based on her own crit damage, and you have a rather scary support for the most powerful DPS characters in the game. Personally, I'm planning on running her with Qingque, since Sparkle is especially potent in a mono-Quantum setup, due to her skill that increases partywide attack based on having other Quantum characters in the squad.

She might not be the DPS star of the 2.0 update like Black Swan, but Sparkle is perhaps even more valuable. Like Yukong, it's hard to pass up a crit-boosting Harmony character, since they'll provide value in any team you shove them in. All that said, here's my best build for Sparkle in Honkai: Star Rail.

The best Sparkle build

Sparkle's main strength is being both a crit-booster for your squad and an invaluable support character for skill-point hungry damage-dealers like Inhibitor Lunae or Qingque. She increases the max number of skill points available to six, recovers four skill points with her ultimate, and buffs party damage when other characters consume skill points. 

Sparkle is the ideal mono-Quantum support character; she provides up to 30% increased attack based on being in a team with other Quantum characters due to her Nocturne bonus ability. A strong Sparkle build focuses around increasing her crit damage and energy regen rate, so she can provide powerful buffs and use her ultimate often, while adding bonus effects to the party via her Light Cone and relics.

• Light Cone: Earthly Escapade or Planetary Rendezvous

The best Light Cone for Sparkle is her signature, Earthly Escapade, which is available alongside her. This five-star gives a 32% bump to crit damage, increasing the buff her skill provides, and also adds another stackable to the mix called Mask. The wearer receives Mask at the start of a battle for three turns, increasing their allies' crit rate by 10% and crit damage by 28%. For every skill point the wearer recovers, such as through Sparkle's ultimate, they gain one stack of Radiant Flame. At four stacks, this is converted into more Mask for the wearer. 

It's a slightly complicated Light Cone effect, but essentially if Sparkle is using her ultimate to get skill points, she'll get Mask often and buff her allies' crits even more. If you already have it, a solid second choice would be Bronya's Light Cone, But the Battle Isn't Over. This buffs energy regen rate by 10% for more ultimates and regenerates an extra skill point every two ultimates, which means Sparkle would recover five skill points every second ult vs. four.

It also gives 30% increased damage to the next ally that acts after the wearer uses their skill, synergising nicely with Sparkle's skill that buffs crit damage and advances an ally's action forward by 50%. For four-star Light Cones you have a couple of options. If you're using Sparkle in a mono-Quantum team, which you should be, Planetary Rendezvous will grant increased damage, while Past and Future is basically just the secondary effect from Bronya's Light Cone, granting extra damage to the next ally that acts after the wearer uses their skill.

• Relics: Messenger Traversing Hackerspace (Four-pieces equipped)

The best relic set for Sparkle is Messenger Traversing Hackerspace. Since there are no relic sets that provide a straight crit damage boost, you're better off using this set to buff Sparkle's speed. Two-pieces will buff speed by 6% while four-pieces will grant allies 12% increased speed when Sparkle uses her ultimate, allowing them to take advantage of the damage boost she provides by acting faster.

In terms of primary stats, crit damage is most important, so you should look for that on the chest-piece if possible, while getting a speed bonus on the feet is ideal if you want Sparkle to act lots. Energy regen is also valuable so she can use her ultimate plenty, and you'll want at least 20% effect res if you're using Broken Keel to get that extra crit damage bonus for the squad.

• Planar Ornaments: Broken Keel (Two-pieces equipped)

There are two pretty good Planar Ornament sets for Sparkle. The first is Broken Keel, providing 10% effect res and a buff of 10% to allied crit damage when you reach 30% effect res. That extra crit damage is very useful for Sparkle's skill, but effect res is also a strong stat for reducing the chances of her being incapacitated.

Your second choice is the Penacony, Land of the Dreams set, though this relies on you running Sparkle with another Quantum character. This increases energy regen rate by 5% while buffing damage for all other allies of the same damage type by 10%. Unlike Broken Keel, you don't have to build any stats to unlock that condition, so this might be preferable in an all Quantum team. For stats, the most important is energy regen rate on the Link Rope, and then best option for the sphere is Quantum damage boost.

Sparkle abilities and Eidolons

Here are Sparkle's abilities, unlockable bonus skills, plus the Eidolons you can get by rolling extra copies of her—thanks Honey Hunter for the details:

Sparkle Ascension materials

Here's what you'll need to ascend Sparkle besides XP materials:

• 15 Tatters of Thought
• 15 Fragments of Impression
• 15 Shards of Desires
• 65 Dream Flamer
• 300,000 credits (approx)

You can get Tatters of Thought via the new Penacony assignment called Tranquillity of Vimala-Bhumi, as well as through all three of the new Golden Calyx on Penacony if you want to earn some XP materials or credits at the same time. You'll then be able to craft the higher-tier Fragments of Impression and Shards of Desire that you need.

The Dream Flamer material comes from the Crimson Calyx, Shape of Roast, on Penacony in the Dreamscape. Lastly, if you need credits or XP materials, you can always farm them via each of the Golden Calyx.