Xu Fu

Xu Fu’s kit primarily is focused around Arts Support and NP gauge refill. Each skill has one boost to NP refill on it, allowing Masters more flexibility as to when the flat charge on her third skill is needed. Most Masters will pop the first two skills on the first turn to enable Arts looping, and then the third whenever they need a 30% gauge boost. Skill order suggesting is 3 -> 1 -> 2 in order to boost NP gain as best as possible.

• Farming Veneration B acts as a key ingredient to looping, giving an NP Gain Rate boost high enough to match Caster Altria’s for the entire party. While it does have a heal and a debuff removal on it, those likely will not be used due to this skill almost always getting popped on the first turn. This should be leveled second as NP Gain is more likely to be multiplicative, and max if planning to use her for loop support. 
• Taoist Technique (Foreign) A gives several key boosts to the party. For looping, it boosts Arts performance making Arts Noble Phantasms regenerate more NP Gauge. It also is her main Crit steroid for the party, something missing from typical Caster Altria looping setups. Its undead damage niche is nice, but not necessary. And Critical Chance reduction on the enemy is rarely important, especially with how low the reduction is. This can be leveled last, but is still important to get maxed out to maximize her looping supportive capabilities.
• The Legend of Xu Fu C contains two main portions. The first is the more common usage, a 30% charge to any target. This is used to fill the NP gauge of an ally when the refund wasn’t quite enough. The second is Consort Yu simping. By giving Consort Yu extra NP damage and a 20% gauge boost on top of the 30% she already received, she can deal out a bit extra for minimal cost. The buff removal is rather trivial, but can still come in handy for difficult content. This charge scales with level so should maxed out first.

“I like Lady Yu and what Lady Yu likes. That's all. Next question.”

In the world of simping, one simp rules above all: Xu Fu trying to get Yu Mei-ren. With a kit meant to be flavorful with its Yu support, Xu Fu actually winds up being one of the best Arts Support Servant around, with extra simpery to Yu.

Xu Fu’s main role in a team is to be a budget NP charging boost. With Farming Veneration B giving the party a large NP generation rate buff and a flat 30% charge available in The Legend of Xu Fu C, she can easily push some Arts damage dealers to looping levels of refund. She’s also an amazing Critical support, with her Noble Phantasm This Is The Elixir Of Eternal Life (that’s a lie) dropping a ton of stars every turn and Taoist Technique (Foreign) A giving the party a soft boost to Critical damage. It also must be mentioned that with Lancer Consort Yu she serves as an especially excellent support.

Sadly, Xu Fu is not long for this world. With no hard defenses and a 3-star HP pool, she can easily be removed from the field with a bad critical hit or a Noble Phantasm from the enemy. All her focus on support also makes her horrific with damage, dealing low damage on face cards and having no burst to speak of. Sadly, her Noble Phantasm is oftentimes hard to access as well.

For a newer Master, or one worried about party cost, Xu Fu is an excellent addition to a team looking to use Arts looping with a budget. Combined with a support Caster Altria, many Arts Servants will be able to use 3 Noble Phantasms in three turns. For a 3-star cost, this simp is all right!

NP Recharge Support

Xu Fu is an excellent support in refilling Noble Phantasm gauges. With a NP gain buff for the party equivalent to Caster Altria’s, a 30% targeted charge skill, and a weak party-wide Arts buff, she gives much of the refund needed to push some damage dealers over the threshold needed to loop. Her easy accessibility and her 3-star cost only accentuates these benefits. 

Critical Support

Xu Fu’s Noble Phantasm contains a massive drop of Critical Stars, at 20 total. With even a small star absorb skill, an ally should be able to take them and near guarantee a Critical hit when necessary. In some cases, just having the Critical will be enough as it will allow for a large NP refund. But when a Master wants to use a Critical Arts card for damage, they can also take advantage of her 30% Critical damage steroid to the party. 

Yu Simpery

Xu Fu’s third skill is decent enough as a 30% charge skill, but it is meant for flavor by boosting Consort Yu’s abilities. For the Lancer version it works perfectly as it will give her 50% extra charge on top of her own 20%, as well as boosting her already highly damaging Noble Phantasm multiplicatively. With NP gain boosts, she may even unlock the ability for Lancer Consort Yu to use multiple Noble Phantasms in a 3-turn round despite being a Single Target DPS. On the flip side, Xu Fu does not work quite as well with Assassin Yu. Because the Assassin version has a Buster Noble Phantasm, she’s only going to benefit from the Noble Phantasm damage boost instead of any of the NP gain buffs. Further, the Assassin’s strengthening on her second skill makes Xu Fu’s buff removal pointless in simpery. It also is quite frustrating to have a 20% starting append charge for Assassin Yu, followed by a 27% self charge and Xu Fu’s 50%, and still being 3% short of a NP.

Low Survival

Xu Fu does have one of the higher HP pools for a 3-star Servant, but in the end, she is still a 3-star Servant. With no hard damage negation, she could be removed from the lineup in one or two bad hits. She does have the ability to heal, but likely will not have access to her first skill as she usually pops that turn one, and her Noble Phantasm’s usage is rare enough that healing is likely not to come from it. 

Horrific Damage

With no damaging Noble Phantasm and a kit meant entirely to support, she will not be doing damage herself. Enough said. 

Hard to Access Noble Phantasm

With Xu Fu primarily acting as a support, she has very few ways of accessing her Noble Phantasm. Her charge is targeted and rarely ever will go to herself, and her cards are so weak Masters will not want to use them if it can be helped. Because of this, her best chance at a Noble Phantasm comes from starting gauge CEs.

Xu Fu may be great at giving out charge, but her own NP gauge will often struggle to fill. Because of this, Starting NP Gauge CEs are the way to go in order to get her NP active as soon as possible. As a support, she also does quite well with Bond Boost / Event CEs to hold. Her Max Bond CE also serves to close in her deficiencies. Target Focus Up CEs may also help to make use of her skills and then have an enemy kill her.

• Great Marshal of Magic / Kaleidoscope / The Imaginary Element / Winter Crystal / Dragon’s Meridian: Xu Fu’s Noble Phantasm is excellent, but it is hard to reach. Giving her a starting gauge CE will make filling the gauge far easier. CEs which boost HP are preferable to pure Attack ones for Xu Fu. 
• Chaldea Lunchtime / Great Detective Foumes / Twin Tail: Without a starting gauge CE, Xu Fu doesn’t provide much to the party outside of her skills. Having her boost drops and bond would be an excellent choice in that case. Note - Twin Tail is an example of an event CE, not a CE she should use normally.
• No Time to Die: If a Master wants Xu Fu to stick around, her max bond CE is quite powerful giving her a Guts. Beyond that, it also gives a bonus 30 stars when the Guts effect is triggered. 
• Outrage / GUDAGUDA Poster Girl: On the other hand, if a Master wants Xu Fu to cast her skills and then get out of the way, a CE which makes all enemies target her would be best. Outrage has the benefit of not giving Xu Fu extra HP, but Gudaguda Poster girl gives a bit of leeway as it keeps focus on her for 3 turns instead of 1.