Okita Souji

While Okita’s skill recs are based on using her in a double Koyanskaya and Oberon system, a double Skadi system will be close to the exact opposite. Masters will typically use Zettou either turn 1 and 3 with double Koyansakaya, or turn 2 with double Skadi to hopefully reach 50% charge, and then Shukuchi and Mind’s Eye either turn 1 and 3 with double Koyan and turn 3 with double Skadi. 

• Shukuchi B is a one turn burst Quick boost for Okita, providing a burst of damage. It is fairly vanilla as a skill but has a low enough cooldown to be loopable with double Koyanskaya. It is advised to use this on turn 3 in a traditional 3-turn setup. This can be leveled last for Koyanskaya setups to at least level 6 for cooldown reduction, or second for Skadi setups to max. 
• Zettou A when upgraded from Weak Constitution A gives Okita a critical gather, critical damage, and a 30% NP gauge charge. This skill is crucial to any loop setup due to the 30% charge. This skill in a double Koyanskaya setup could  be cast on turns 1 and 2 but is typically cast 1 and 3 as the third phase of a boss is typically hardest. Level this first and to max.
• Mind’s Eye (Fake) gives Okita her 1-turn evasion as well as a Critical Damage boost. This skill provides her biggest burst of damage in a Buster Crit setup, so the evasion typically is ignored. With double Koyanskaya Criticals are more important so this should be leveled second and to max to reduce the cooldown enough, while with double Skadi this can be left to last and raised to any level desired.

"Okita-san daishouri! No worries, I still have the strength to continue--(gurgle)”

As a member of the Shinsengumi, Okita Souji was once feared by all of Kyoto. As a member of Chaldea, she is a woman constantly coughing up blood while looking suspiciously like Altria. But she is also an amazing Single Target Quick damage dealer with the potential to become a Buster Critical damage dealer.

With her interlude giving her a 30% NP charge, Okita can now function best in two separate ways. First, a Master can buff her Quick damage with Skadi supports, using Shukuchi to buff Quick further in a burst turn to kill a boss and potentially get some Quick Crits after. Her second way is now available with her buff, which is to use her with Double Koyanskaya and Oberon to take advantage of her Critical damage with her Noble Phantasm being secondary. Thanks to the cooldowns of Zettou and Mind’s Eye (Fake), she can boost her Critical outputs twice and ensure she gets her stars on turns 1 and 3. 

Of course, Okita is highly support reliant to use at peak, and lacking a support can hurt her damage potential significantly. As a Single Target Quick unit, she also has rather lackluster refund so most refund will have to come from her cards instead (in both usage scenarios). 

Okita-san daishouri will be a phrase Masters hear a lot when using her, because she defeats bosses. She’s an excellent addition against all Lancers.

Good Sustained Damage

Thanks to Okita’s 30% charge, she can now operate with casting a Noble Phantasm every turn without relying on specific cards, and with better Craft Essences. While this Noble Phantasm damage is reduced, it comes with major damage increases to her Buster criticals while still keeping her other Criticals high. Turn 3 Criticals benefit from an additional 90% damage up thanks to this buff.

Good Card Hit Counts

Okita has a very high base NP gain rate, allowing her Quick cards to generate a large amount of Noble Phantasm gauge. For refund situations typically involving Skadi, she can use this to fill the gauge still missing. Her hit counts also allow for decent Crit Star generation from her Quick Cards.

Durability

Okita’s third skill gives her a 1-turn evasion to counter a boss’s big attack, and also has a relatively high health pool. She may be able to survive a number of hits before succumbing to the TB.

Support Reliant

Without proper supports, Okita is typically outclassed by free and cheaper Servants. Her shine comes due to her support compatibility, giving 2 distinct methods of use.

Poor NP Gain on Noble Phantasm

Okita only has 3 hits on her Noble Phantasm. This, even if buffed, will give her nowhere near the 50% gauge she’d need to loop with a double Skadi system, not even the 30% for double Skadi and Oberon. She needs to rely on cards for refund, which may not always be available.

Okita has turned into a looper depending on the scenario. In a double Koyanskaya and Oberon setup, she benefits the most from Mixed Starting NP Charge / Critical Damage CEs. In a double Skadi system, Oberon optional, she benefits the most from Starting NP Charge CEs. Without either setup, she can also benefit from NP Damage Up CEs to get a good burst of damage.

• Holy Night Supper / The Queen Priestess's Spare Moment / Cosmo Chaldea High School / Empty Garden / Blooming in the Crimson Sky / A Tale of Love and Hope / Starry Nights - ANY CE which boosts Critical damage while giving NP gauge is decent on Okita to take advantage of her stacking crits. Holy Night Supper is special for also increasing Noble Phantasm strength, and The Queen Priestess's Spare Moment boosts the double Koyanskaya target of Buster crits by 35% at MLB!
• Kaleidoscope / The Imaginary Element / Golden Sumo: Boulder Tournament / Knights of Marines / Traces of Christmases Past / Dragon’s Meridian - To guarantee a loop with double Skadi and Oberon, Okita requires a Kaleidoscope. Anything lower than that, she is relying on refund from cards on wave 1 or 2. These do give early access to her Noble Phantasm in all situations, however.
• The Black Grail - As a damage dealer, simply sticking a Black Grail on Okita and letting her go off can provide a strong 1-turn burst at the cost of sustainability.