Disclaimer: The information below are speculations based honeyhunter's website that uses data of unreleased characters. These are subject to change when they are officially released.
Hu Tao is a Pyro polearm user that can use her HP to boost her attack and damage. Since she has high base HP, it can be pretty easy to reach over 30,000 HP with some HP% mainstat artifacts, making her quite tanky that can still hit hard. However, she has very low base attack, making her very reliant on a good weapon to equip. She will be able to deal high damage when her skills are up, but not be able to do much when it's on cooldown.
Having low base attack will mean going with attack% stats won't be good on her since it will give low returns. Focusing on HP% main stats and substats, as well as crit rate/damage will be ideal. Her elemental skill makes her normal attacks into Pyro, so the 2 piece Crimson Witch of Flames will be useful with another 2 piece bonus like Noblesse Oblige or Wanderers Troupe will be good. Otherwise, full 4 piece Lavawalker might potentially be the best go to choice for her.
If you only want to focus on her normal and charge attack damage, Heart of Depth 4 piece bonus can be a good option, even if the 2 piece bonus is wasted. 4 piece Retracing Bolide also works because it gives higher bonus, but it comes with a requirement that can be difficult to manage
For weapons, Staff of Homa is a weapon that's rumored to be released with Hu Tao's banner, and it will be her best in slot weapon. Crescent Pike has high potential to be the weapon of choice other than staff of homa. Otherwise, it's recommended to go with a weapon that gives crit related secondary/passive because her ascension bonus is crit damage.
Pairing her with Xingqiu can potentially be strong because the rain swords applies Hydro constantly. The skill will also reduce damage taken, making it less risky to play with around 50% or less HP for the damage boost.
Kaeya can be a good character to consider. Since polearm characters attacks pretty fast, you might not be able to get constant x2 Melt from Hu Tao using Kaeya's burst, but you will be able to get the x1.5 Melt instead, which still deals some pretty good damage. The crit rate increase from Hu Tao's first ascension bonus will also help Kaeya deal more damage since most Kaeya builds are often crit related.
Zhongli will be a good support in general. The shield will make it safer for Hu Tao to keep attacking at 50% hp or less, and Zhongli's shield also reduces enemy's RES by 20% to make Hu Tao deal more damage. Using a Geo character can also mean that you can give the Geo character Archaic Petra for the 4 piece bonus, and Retracing Bolide for the main DPS character.
Commands blazing spirits to attack, dealing Pyro DMG in a large AoE.
Upon striking the enemy, regenerates a percentage of Hu Tao's Max HP. This effect can be triggered up to 5 times, based on the number of enemies hit.
If Hu Tao's HP is below or equal to 50% when the enemy is hit, both the DMG and HP Regeneration are increased.
Supernatural activity by those who have already left this world is a source of great anxiety for the Wangsheng Funeral Parlor. In such cases, cremation always lets Hu Tao find peace of mind. The more anxious she feels, the stronger the flame.
The More the Merrier
When Hu Tao cooks a dish perfectly, she has a 18% chance to receive an additional "Suspicious" dish of the same type.
When Paramita Papilio state activated by Guide to Afterlife is over, all allies in the party (excluding Hu Tao herself) will have their CRIT Rate increased by 12% for 8s.
When Hu Tao's HP is equal to or less than 50%, her Pyro DMG Bonus is increased by 25%.
While in Paramita Papilio state activated by Guide to Afterlife, Hu Tao's Charge Attacks do not consume Stamina.
Increases the Blood Blossom DMG by the amount equal to 4% of Hu Tao's Max HP at the time the effect is applied. Additionally, Spirit Soother will also apply the Blood Blossom effect.
Increases the Level of Guide to Afterlife by 3. Maximum upgrade level is 15.
Garden of Eternal Rest
Upon defeating an enemy affected by Blood Blossom that Hu Tao applied herself, all nearby allies in the party (excluding Hu Tao herself) will have their CRIT Rate increased by 12% for 15s.
Increases the Level of Spirit Soother by 3. Maximum upgrade level is 15.
Triggers when Hu Tao's HP drops below 25%, or when she suffers a lethal strike: Hu Tao will not fall as a result of the DMG sustained. Instead, all of her Elemental and Physical RES is increased by 200%, and her CRIT Rate is increased by 100% for 10s. This effect triggers automatically when Hu Tao has 1 HP left. Can only occur once every 60s.
A Stella Fortuna is required to unlock each constellation. See Constellations Guide for more details.
The Wangsheng Funeral Parlor is a reputable institution that acts with integrity. But whenever I see that cheeky smile that says, "it's nothing you exorcists need to worry about," it just makes my blood boil... Whoa, deep breaths Chongyun. Stay calm.
Is Hu Tao picking on you too? Ugh, that prankster always waits till I least expect it, creeps up on me from behind and then... Boo! ...then laughs herself silly. Hmph. But I can handle it, and she does bring me fermented plum blossoms once in a while so I can make flower cakes... so I don't hold a grudge.
Ah yes, the young lady who is now the master of the Wangsheng Funeral Parlor. If you're asking what I think about her as a person... Well, there are all sorts of rumors about the way she works. But I think if you really want to understand someone, you need to find out what they are really after.
The current overseer of the funeral parlor? Ahem. I cannot deal with that child.
Hu Tao In Bulletin Boards
Wangshu Inn Buletin
Guest Message: "Thank you for the stay. My scholar friend of Sumeru and I talked happily into the night, from debating the principles of the world and elements to recounting stories of our hometowns, famous specialties, culture, and nearly every topic one could think of — reminiscing like this really makes one's heart swell with emotion"
"I should be getting back to the Wangsheng Funeral Parlor after the rain stops, otherwise Master Hu may come drag me back herself."
Reply: We hope you enjoyed time here and look forward to your next visit. Also, please tell your friends in Liyue Harbor about our wonderful establishment.
Feiyun Slope Bulletin Board
Message: "If any residents see a zombie child out in the middle of the night, doing stretches or gathering herbs on the mountain, please don't be alarmed. Her name is Qiqi. She's a student of medicine who helps out at the Bubu Pharmacy, and she's completely harmless."
"—Baizhu, Bubu Pharmacy"
Another Note: "Life and death are up to fate. Why delay the inevitable? Why suffer to live alongside one who should already be dead and gone? Bring Qiqi to the Wangsheng Funeral Parlor and we will provide a comprehensive, stress-free funeral service that safely and respectfully returns her to the elements. Wouldn't that be grand?"
"I've no clue what she's thinking, going around looking all happy-clappy like that when she's the head of the Wangsheng Funeral Parlor. Always greets me cheerily too, saying "I like people who play with fire, they're good for business" or somethin' like that... She's a bit bizarre, I tell you."