Sei Shounagon (Berserker)

“Wack, man, that's wack.”

When Sei decided to become a swimsuit Servant, she became a Berserker! To her, however, this meant she’d become a delinquent, and created one of the most deceptive kits around. While at a first glance she seems like she should be a Quick-Oriented Man-trait SingleTarget killer with her Noble Phantasm, reality is that she is truly a Buster Crit-Oriented Single Target murderer.

How, a Master may ask, is a Servant with a Quick Noble Phantasm actually a Buster Servant? Simply put, Sei comes with a kit complete with three Buster cards and only one Quick card. Further, her skills are designed around boosting her Critical damage, given Summer Street A’s sustained Crit boost, Night Pool Slider’s burst Crit boost, and For You - Summer Sweet’s star bomb. Further, these are all on low enough cooldowns to use twice in two turns with proper setups. Altogether, they can add up to massive damage, added together with her Noble Phantasm’s bonus traits against Man, Lawful, and Shadow Servant type enemies (and decent damage to go with it).

Delinquent life does have its downsides, and Sei is no exception. Like all Berserkers, she is naturally squishy and will need protection to survive. Further, she is quite burst-oriented, with her damage significantly falling off after 1 or 2 turns. She also doesn’t have easy access to her Noble Phantasm with only a 20% charge to help her.

Sei is a wonderful asset against bosses with a single break bar, especially those who hit her trait bonuses of Man, Lawful, or Shadow Servant. But by requirement, the Master who summons her must be ready to be a true rebel.

Critical Damage

Sei’s Crits can be quite devastating with the combination of a 30% sustained Crit bonus, and a 100% one-turn Crit bomb on her second skill. This becomes even more noticeable when she runs with a double Koyanskaya of Light setup, boosting her already decent Buster Crits by massive amounts and providing large star bombs and Man bonus damage when needed. She may eventually do more damage with her Buster Crits than her Noble Phantasm with the right setup. 

Low Cooldowns

Sei’s first and second skills have a 6-turn cooldown and her third skill a 5-turn cooldown. While this is impractical for Masters without a Koyanskaya of Light, those with one can use her charge skill and an Atlas Mystic code to reduce these to 0 on the second turn. This allows for Sei to have two turns of massive Critical Damage against her enemies. 

Trait Bonuses

Sei covers a wide array of traits, including the common Man-trait and Lawful-trait, along with the rarer Shadow Servant trait. Admittedly, there are not many break bar or tough Shadow Servants to deal with in the game, but the first two are all too common and often stack with each other to provide massive damage boosts. These bonuses are activated for 1-turn on her Noble Phantasm, so if she crits after casting her Noble Phantasm, the Crits will be boosted as well. Note that since these are powermod bonuses, they stack additively to Crit damage instead of multiplicatively.

Squishy

Sei is still a Berserker, regardless of everything else. She has a low health pool and takes double damage from almost everything. While she does have a 2-hit 3-turn evasion, this may not be enough especially against some AoE-type bosses. Her heal on her third skill may be entirely ineffective as she may already be dead. 

Poor Sustain

While Sei has a great burst which can be extended to two turns with Koyanskaya of Light, once it ends she has nothing but a small Attack and Crit bonus left to work with of her own. The 5/6 turn cooldowns on her skills begin to look endlessly long against her low health pool after that. 

Low NP Gain

Sei only has her single 20% charge skill to boost her gauge, and as a gorilla type Berserker she has only one average Arts card to work with to get gauge back. Any Noble Phantasms from her will have to come from outside sources.

Everything about Sei’s kit is about her Crits, and anything that is not about her Crits is practically ignored. She is designed to pop all three skills at once and provide a massive barrage of damage, both through her Noble Phantasm and her Critical hits which follow. That said, it is still recommended to level her 1st skill first to get easier access to said Noble Phantasm, followed by 2 and then 3 for Crit priorities.

• Summer Street! A is the closest thing Sei has to a sustain, giving small boosts to Critical damage and Attack for 3 turns. However, this also offers her a 20% charge and allows her to benefit from 60% Starting Charge Craft essences if her Append 2 is maxed. Due to this, it should be leveled first and to max. 
• Night Pool Slider A is Sei’s burst skill, giving a whopping 100% Crit damage buff at max level and practically guaranteeing all Stars will go to her. This skill of course should be popped when Sei has the Card to use a big Crit on. It also provides Sei her survival kit, giving a 2-time evasion over 3-turns. This skill has the largest damage gains so should be leveled second, and if using double Koyanskaya of Light and an Atlas Mystic Code must be leveled to at least level 6 to reduce the cooldown. However, max level is recommended. 
• For You - Summer Sweets A is the weakest of Sei’s skills, primarily used for its ability to generate stars for the turn. While it does provide a small heal and a relatively useless burn immunity, these tools are not practically used in most fights. This is best used when Sei wants to crit but doesn’t have the stars to do so. This should be leveled last to at least level 6 to reduce the cooldown.

Sei’s Craft Essences should primarily focus on further boosting her damage, especially of Buster Cards and Crit. By far the best CEs are those with Mixed 60%+ Starting NP Gauge / Damage or Crit. These cards are rare, so lacking that Masters want easy Noble Phantasm access with Starting NP Gauge CEs. Attack Up CEs can also be situationally useful.

• Summer Anniversary / A Tale of Love and Hope / Partake with the King / Teacher and I / : Sei is designed for a 2-turn damage burst with double Koyanskaya of Light. With a 60% Starting NP Gauge, a maxed Append skill 2, and her first skill, she will be able to cast her Noble Phantasm turn 1, and then use the double Koyanskaya setup for a second on turn two. Even without double Koyanskaya, these still guarantee her at least one Noble Phantasm for its damage and powermod for the turn. All CEs listed are centered around Buster of Crits and must be MLB to work. 
• Kaleidoscope / The Imaginary Element: Any 60%+ charge can act the same way as the ones listed above, however without the bonuses to damage. The Imaginary Element is notable in that it doesn’t have to be MLB to work here. 
• Gudaguda Poster Girl / Code Cast / Golden Sumo: Boulder Tournament / Bronze Link Manipulator: Sei will likely be getting plenty of Buster support from her allies, and Crit damage will only give additive effects, so the best way to increase her damage is through Attack bonuses. While Gudaguda, Code Cast, and Bronze Link Manipulator are only for 3-turns, Sei is a Burst Servant and will not need longer than that. Sumo has the bonus of a starting gauge, but one which will need further support to fully utilize as it is only a 50% start.