Ittomiya

Ittomiya is the het ship between Arataki Itto and Naganohara Yoimiya from the Genshin Impact fandom.

Canon
The two currently do not interact in the game story or events. Although, information about their relationship exists through their voicelines and personal information.

Voicelines
Yoimiya has two voicelines about Itto. In the first one, she mentions that Itto, despite his scary appearance, is very popular with kids, just like her. Aside from that, she also states that Itto is also very competitive (since he thinks every battle should be taken seriously) and when both of them are playing with the kids together, it always turns into a showdown between them.

They would try, for example, eating a bowl of ramen soup in one go, or try to eat sour plums without making any strange faces. The children who are presented will try to guess the winner, which pressures both characters to try to win the competition immediately.

Yoimiya's second voiceline about him implies, in a surprised tone, that she didn't know he was part of a gang, and it also says she thought he just had a lot of free-time. Curiously, Itto doesn't seem to know that Yoimiya didn't know he was part of a gang, or he simply just never mentions it.

Similarly, Itto's voicelines mention that Yoimiya is always showing off her fancy fireworks and toys to the kids, which makes Itto envious and "sick of it". He tells the traveler that nobody should be allowed to steal his "thunder" and he is the one that's supposed to be adored by the kids, which also goes for the traveler, and he also states that they should stay on his side on this instead of Yoimiya's.

Character Story Profiles
Yoimiya's Story in Story 4 mentions that Yoimiya's "second career", which are her distinctive handicrafts and practice works that her personally-made toys, which are inspired in the games of common people, are adored and very popular alongside the population of Inazuma, especially kids, and even adults, and later mentions that Itto adores them as well.

The head of the Arataki Gang comes over to buy her specially-made knickknacks, which he then brings to go challenge the one he has declared his nemesis. Interestingly, the story also mentions that Yoimiya made a somewhat-failed "Onikabuto Chariot toy".

Given the attachment that Itto has on Onikabutos, it can be theorized that Yoimiya's failed chariot was going to be given to Itto, or at least was linked to him, since the story mentions him later. It could be also be a spoiler for Itto, since he was released months after Yoimiya and was first introduced in her voicelines, being theorized at first to loving beetle tournaments.

Miscellaneous
In the "The Almighty Arataki Great and Glorious Drumalong Festival" Event, Yoimiya noticed the Arataki Gang getting the venue ready for the Almighty Arataki Great and Glorious Drumalong Festival when she was there to deliver some fireworks, and she got curious and went to go check it out, according to an NPC in the event, Hirohiko.

Itto talks about Yoimiya when you ask him. He says, "Chatting with her is a real blast. She only found out about our festival because she happened to be delivering some fireworks to Amakane Island. She really liked what we're trying to do here, and came to pass on her best wishes. She even said she'll provide some fireworks for us next time." He adds, smiling, that "the Arataki Gang should make sure to keep good ties with Naganohara Fireworks in the future."

Yoimiya also leaves a message for the Arataki Gang in the bulletin board in the festival. She says that although it's not the liveliest of festivals, the festival is magical in its own way, and says, "Go, go, Arataki Gang! Let me know in advance next time and I'll get you some fireworks, free of charge!".

Quotes
"Oh, he may look scary, but he is very popular with the children. However, he can be very competitive. Every time we play with the children, it always turns into a showdown between him and me. For example, we'd drink a bowl of ramen soup in one go, or try to eat sour plums without making any faces. The children will cheer us both on and try to guess the winner. And when that happens... well, then I can't let him beat me, right?"

- Yoimiya's Voiceline about Arataki Itto

"Arataki's gang? Huh!? So he isn't just someone with too much free time on his hands?"

- Yoimiya's Voiceline about Arataki Itto II

"Hmph, she's always showing off her fancy fireworks and toys to the kids. Well, I'm sick of it! Nobody steals my thunder! I'm the one that's supposed to be adored by the kids! Me! That goes for you too, you're siding with me on this, okay... Huh? Whaddya mean, you're not a kid? Eh, details. If you're shorter than me, you're a kid as far as I'm concerned."

- Arataki Itto's Voiceline about Yoimiya

"Chatting with her is a real blast. She only found out about our festival because she happened to be delivering some fireworks to Amakane Island. She really liked what we're trying to do here, and came to pass on her best wishes. She even said she'll provide some fireworks for us next time. Looks like the Arataki Gang should make sure to keep good ties with Naganohara Fireworks in the future."

- Arataki Itto on Yoimiya's reception of the festival, The Arataki Great and Glorious Drumalong event

"I was surprised to find someone hosting a festival tucked away in a little corner of this island, especially a new festival that I'd never heard of. The view here is amazing. Although it's not the liveliest of festivals, it's magical in its own way. Go, go, Arataki Gang! Let me know in advance next time and I'll get you some fireworks, free of charge!"

- Yoimiya's message to the Arataki Gang, Amakane Bulletin Board

Fanon
Ittomiya is a small ship within the Genshin Impact fandom, being considered a rare pair. The fans of this ship mostly like the dynamic of the duo, especially since both characters are shown to be very enthusiastic and friendly, and overall, very energetic.

Their matching personalities and funny contrast are often portrayed in fics, since they are seen as a comedic pairing. Those who don't see their dynamic as romantically enjoy their dynamic as best friends or as a found family, sometimes making Yoimiya part of his gang.

The ship is usually overshadowed by more popular ships with both characters. Its rival ships are IttoSara and IttoGorou, which are some of Itto's popular ships, and Ayamiya, which is one of Yoimiya's popular ships.

Fandom
FAN FICTION

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Trivia

 * Itto and Yoimiya's birthdays are in the month of June.
 * Both are residents of Hanamizaka. While it's unclear where Itto lives, exactly (due to his Serenetea Pot lines insinuating he's homeless), Onibaba is a resident of the district and Itto's constant association with the area implies it's his hometown. Meanwhile, Naganohara Fireworks and the family home is located in Hanamizaka.
 * Both characters have a gigantic bow on their backs in their respective designs.
 * For the 2021 Game Awards, Genshin Impact won the Best Mobile Game award. Mihoyo made an entry video during the ceremony where both Yoimiya and Itto were featured.
 * In the video, Yoimiya is running towards Itto, seemingly at the start of a competition between them and the kids, who are jumping and cheering for them in the corners. Itto states that he is the one who should be adored by the kids, a reference to his voiceline about Yoimiya, and Yoimiya replies, in a humorous tone, "Not if I have to say anything about it".
 * The first day of the Almighty Arataki Great and Glorious Drumalong event featured the song "Blossoms of Summer Night", Yoimiya's theme, as the first song to be played. At the end of the event, it was the most-frequently played song out of the tracklist.