Itthoma

Itthoma is a slash ship between Arataki Itto and Thoma from Genshin Impact.

Canon
Prior to the Irodori Festival, while neither had met in person, their voicelines indicate they had at least heard about the other. Thoma seemed fascinated by Itto and his Youkai heritage, and expressed the wish to befriend him. Itto, conversely, was chagrined that Thoma had been chosen for the Vision Hunt Ceremony and demanded to know what made him important enough to be chosen.

In addition, Itto is canonly friends with Ayato Kamisato, one of Thoma's bosses and close friends, which implies Thoma likely heard about Itto through that channel.

Their past histories also draw parallels between the two.

Thoma was originally born in Mondstadt to an Inazuman father and Mondstadt mother, but when he was in his teens, his father suddenly disappeared and returned to Inazuma. While what became of his family is unknown, Thoma tried sailing across the sea to Inazuma to bring his father some of his favored Dandelion Wine, but was capsized, washed ashore, and forced to fend for himself until the Kamisato Clan took notice of him and gradually brought him into the clan where he worked up the ranks to become the Kamisato siblings' close friend and retainer. Despite this, Thoma still struggled with being an outsider and even has a bit of a negative reputation due to the connections he has that leads to some fearing he could use those connections in underhanded, malicious ways that makes many fear the notion of double-crossing the Yashiro Commission.

Itto, too, had a difficult past when he and his parents were often pinned with blame due to them being Oni and the negative stigma Oni face. After his parents died when he was young, Itto took to the streets for some time and was often beaten up and ostracized due to how loudly he defended being an Oni against any nay-sayers. Like Thoma, he still has something of a negative reputation due to being an Oni and general troublemaker that intimidates local children with threats of snatching their snacks and generally has a troubled reputation due to his antics in the Arataki Gang.

The Irodori Festival
Kimura is worried that some group is hogging the photo board during the festival and the guards were stationed to not interfere. The Traveler accept the request to check the board, only to find a whole group of Arataki Gang trying to enjoy the festival with having no money to spend on something special there.

Their leader, Itto demands the Traveler to have a competition at Irodori Fest if they want to leave the board. The passing Thoma greets the group and suggesting they do a volunteering competition where the help whatever in trouble in the area. At first, Itto is not interested, but knowing the prize is a special limited Rainbow Aster that he wanted, he accepted the deal and got to work. By the instant chemistry the two had, Paimon commented that the two seemed to be developing "a real bromance."

Unbeknown to the Oni, the Traveler just got word on their last request that the prize drink contains soybean milk. And just when Itto drink till the last drop, he crumpled to the ground due to his bean allergies, prompting both Thoma and Itto's gang to escort him to the doctor.

The Almighty Arataki Great and Glorious Drumalong Festival
While Thoma wasn't among those invited, the retainer nonetheless visited and commended the group on their efforts and even offered to help them out the next time the Gang wanted to host another event. In addition, Thoma left Itto two King Onikabuto in a pricey container that implies the closeness he feels with Itto.

Quotes
"Hmm... Word on the street is that he's quite a character — apparently, he even has youkai heritage. Have you met him? If you two are close, maybe you could introduce me sometime. It's good to make friends from all walks of life... youkai included!"

- Thoma, About: Arataki Itto

"Some of the boys have been telling me that he was the star of the show at the Vision Hunt Ceremony. I'm like — are you kidding me??? How come he gets his own special ceremony!? Was the hundredth Vision supposed to be, like, stronger than the other ninety-nine, or something? Pff, nah, it can't have been that, 'cause, uh, hello! They would've chosen me if that's what they were going for."

- Arataki Itto, About: Thoma

"Well, I heard that a certain well-known individual had made an appearance at the festival and taken quite a liking to the Tanuki photo board. Since the Yashiro Commission is the host of this festival, I felt I simply had to come and meet them in person. Red horns... If I'm not mistaken, you must be the esteemed Arataki Itto, leader of the widely renowned Arataki Gang, is that right?"

- Thoma to Itto, About That Time We Saved the Tanuki Photoboard

"Hahahahaha! Thoma, my bro, your eyes do not deceive you! And you are the housekeeper extraordinaire of the Kamisato Clan! You're quite the celebrity yourself, you know."

- Itto to Thoma, About That Time We Saved the Tanuki Photoboard

"Hey, bro! Haven't seen you since the Irodori Festival. I hope you're doing well. I didn't know you were gonna be hosting a huge festival — you sure kept that quiet! Nice work! If you ever wanna host another festival in the future, feel free to come and discuss it with me first. If you need a venue or furnishings or anything else, I'll see what I can do. Everything's negotiable! By the way, I know you like beetle fighting, and I remembered that I had a couple of King Onikabuto at home. I left them on the wooden box over there. Enjoy!"

- Thoma's message, Amakane Bulletin Board, The Almighty Arataki Great & Glorious Drumalong Festival

Fanon
Within the fandom itself, many are keen on the idea of Itto and Thoma being a classic friends-to-lovers romance with Itto often teaching Thoma how to unwind and relax, to embrace the wild side of life. On Thoma's end, many like taking note of Thoma's attentiveness and care for those he cares about and often depict him caring for Itto. Some see Thoma as a mom friend while Itto is more of a dad friend, which means the pair being shipped would make them the 'parents'. On yet another angle, some also like the notion of Itto intimidating Thoma in a flirtatious way due to him feeling challenged by Thoma having a stronger Vision, and playing out scenarios where Itto challenges Thoma, or corners him against a wall and proceeds to flirt that way.

Despite this, the two befriend each other almost instantly and have a generally good relationship with each other, which often leads to them being depicted as having an easy-going and comfortable romance with each other often filled with fun and attending events like festivals.

Sometimes, Itto's friendship with Ayato can come into play, which can lead to the odd interaction of Ayato fooling around with the pair and participating in TCG's and other childish games with them, like Onikabuto Battles.

Within the fandom itself, Itthoma is often rivaled by Ayaitto and Ittorou on Itto's end, while on Thoma's, it's rivaled by Thomato. Currently, it has 120 fanfictions on Ao3.

Fandom
FAN FICTION

TWITTER
 * Daily Itthoma: @dailyitthoma
 * Daily Itthoma: @dailyitthoma
 * Daily Itthoma: @dailyitthoma

Trivia

 * Thoma was among the first characters to encounter Itto in his Character Teaser, appearing near the end where he witnessed Itto crashing a stage-play and telling Ayato to look backstage.