Ittokazu

Ittokazu is the slash ship between Kaedehara Kazuha and Arataki Itto from the Genshin Impact fandom.

Canon
Although Itto and Kazuha have yet to meet in canon, Itto's voiceline about how they're both from fallen clans does indicate some connection between them, and the fact that Itto has heard of him, especially after his feat in blocking the Shogun's signature attack during the Vision Hunt Decree that gained Kazuha a degree of celebrity, especially evident in the beginning of his story quest. While they do have a fair degree in common, there are many differences between them, as well.

Unlike Itto, the Kaedehara Clan was a noble samurai clan known for the Isshin Art, and part of the Raiden Gokuden and one of the five illustrious bladesmithing clans within Inazuma before a series of events roughly a century before the events of the game triggered the clan's steady downfall until its collapse shortly before or during the Vision Hunt Decree where Kazuha became the last Kaedehara. After the decree was through was Kazuha given the chance to restore his clan, which he declined.

Itto's clan, meanwhile, has very little known about it except that they likely had been stricken by poverty while he was still extremely young until his parents died unexpectedly and were prior discriminated against for being Oni. Itto was forced to live on the streets for quite some time as an orphan, often getting mistreated and abused when he tried to defend being an Oni to strangers, all before Onibaba adopted him.

There are some past threads that tie them together, however. Both are connected to the Kamisato Clan, with Itto being a close friend of Ayato, despite presumably being unaware of his status as Clan Head, while Kazuha's clan was their subordinate branch and his friend, nicknamed Tomo, was also a close friend of Ayato and Thoma's.

On a more tragic end, they both bear connections to each other through their respective friends, Sara and Tomo. Although it's more speculation, many fans believe that a young Tengu Itto used to have a rivalry with on the Byakko Plains was none other than Sara herself, but because she was adopted into the Kujo Clan, given a name, and grew up to look quite different from her tomboyish youth, it's believed Itto's Tengu friend and her were one in the same. During the VHD, she was the one who dueled Tomo and won, ultimately leading to his death.

Visions
Perhaps one of the most extraordinary aspects of both characters were what became of them and their Visions during the VHD. As it has shown, those who have their Visions taken quite literally lose a part of themselves and often become listless and depressed, as well as forgetting many memories connected to their ambition that allowed them to acquire a Vision in the first place. Itto, meanwhile, seemed completely unaffected by having his taken and seemed as lively and intact as ever. Kazuha, also, had extraordinary circumstances surrounding him. When he and the Watatsumi Army confronted the Shogun at Tenshukaku, he was able to activate his friend's Masterless Vision for a moment and harness the power of Electro to block and parry her infamous Musou no Hitotachi, being the only example of someone wielding two Visions simultaneously, even if it was short-lived.

Regardless, to the present time is Itto the only one to have his Vision forcefully taken but emerge unchanged, while Kazuha was the only person to wield two Visions in tandem.

Summertime Odyssey
Although Itto clearly wasn't present in the Summertime Odyssey quest, during the last night on the island did Kazuha suggest having Roasted Lavender Melons, a snack that's a signature favorite of the Arataki Gang and especially Itto. When the Traveler mentions they'd had it before, Kazuha asked if they had it in Inazuma, the Traveler goes on to say that a few Inazuman friends, referencing Itto and Shinobu, had made it for them before. Kazuha goes on to say how great that is and wants to follow their example by traveling the world and making many good friends as the Traveler has.

The Almighty Arataki Great & Glorious Drumalong Festival
Again, while Kazuha wasn't present during the Drumalong, his theme song, Drifter's Destiny, was the third track on the event's tracklist and released on the third day of the event.

Miscellaneous
While they haven't met, Itto and Kazuha do share many lifestyle traits in common. Before Kazuha's redemption, both were considered criminals; Itto was through his various antics with the Arataki Gang that land him in prison, and Kazuha as a fugitive on the run from the Vision Hunt Decree before he was redeemed.

From their voicelines and shared favoritism of the Jade Wilds furnishing set, both tend to habituate in nature and live very nomadic lives, even if Itto tends to remain in Inazuma while Kazuha is based on the Alcor when not wandering the land.

Both have an affinity for music as Itto is said to be a good singer as mentioned in his character story, and seems proficient with a drum based on the Drumalong. Kazuha, meanwhile, is noted to be able to use leaves as instruments.

Both are friends of Heizou, as Kazuha is a longtime friend of the detective while Itto met him during Heizou's "Take Em by Storm" Hangout event and seems to have befriended him in the "Heizou Talks Fraud" in The Three Undeceivables ending. Similarly, they are also familiar with Yoimiya as Itto has a friendly rivalry with her to win the favoritism of the local children while Kazuha is known to be involved in the shipment of Naganohara Fireworks now and then.

Physically, they both have red eyes and red streaks in their light-colored hair, though Kazuha's varies between being white and a light, strawberry blond while Itto's is more silver in hue.

Quotes
"Word on the street is that he blocked the Musou no Hitotachi after you escaped from Tenshukaku. Seriously? 'Cause I mean, that is awesome! Who knows how he pulled it off. Hey, now that I think about it, he's from a fallen clan, and I'm from a fallen clan... That kinda makes us equals, haha! Yeah, so next time someone attacks you, it's my turn to block the blade!"

- Arataki Itto, About: Kaedehara Kazuha

"There is a snack called Roasted Lavender Melon in Inazuma, which goes rather well with fish. Why don't we roast some fruit and seafood for dinner tonight?"

- Kaedehara Kazuha, Summertime Odyssey

"This peaceful scene puts the mind at ease. Even the most ordinary stretch of countryside, the humblest of hills, harbors poignant profundities from the distant past. Offer them your full, undivided attention, and each flower, each tree, each blade of grass will whisper their stories to you."

- Kaedehara Kazuha, commenting on the Jade Wilds furnishing set

"Whoa, check it out, this looks just like Granny Oni's place... Pretty sweet. The scenery's really makin' my day! Let's go kick back in the shade. I'll tell you all my epic tales from roaming the wilds of Inazuma!"

- Arataki Itto, commenting on the Jade Wilds furnishing set

"I never stay in a single place for very long. Stagnancy dulls both my connection with nature and the blade I wield. While I am still able to, I want to travel far and wide and meet all sorts of different people."

- Kaedehara Kazuha, About Kaedehara Kazuha: IV

"I've slept on the streets, down at the dock, deep in the forest... Pretty much everywhere! Of course, comfort-wise, the cells at the Police Station are up there at the top of the list."

- Arataki Itto, Companion dialogue

Fanon
As they have yet to interact and their fanbase seems to be extremely small on most platforms, most shippers tend to take note of Itto's voiceline when shipping them on how they could sympathize with each other as criminals (even if Kazuha is now a former one) as well as the sons of fallen clans and the last of their families, notably with Itto believed to be the last Crimson Oni while Kazuha is canonly the last of the Kaedehara Clan.

In terms of rivalry, they tend to compete with the Ittozou and Heikazu ships, though some are fond of shipping the three together. Because of how rare the ship is, it isn't known if they're competed with by other ships, but it can assumed it's too small to catch many shippers' radar.

Even so, they do appear to be a classic case of "opposites attract" due to Kazuha's soft-spoken, poetic personality while Itto is loud and boisterous and rarely able to key in with more complex speech patterns of the kind Kazuha likes to employ. Based on Kazuha's voiceline "Frank Speech," he seems to like those who speak frankly and would presumably take a liking to Itto. Still, as fellow wanderers, some like the idea of them traveling together and exploring the world, among other ideas. Since the end of the Sakoku Decree that kept many Inazumans in and others like Kazuha out, it could lead to more interaction since Itto recently went to Liyue in 2.7 and Kazuha often is based from there due to his adventures on the Alcor.

In addition, with the Arataki Gang's own philosophy of personal freedom and living as one wishes, and Kazuha's own similar values in living boundlessly, it's another point some shippers could find the pair have in common.

Fandom
FAN FICTION

Trivia

 * Both of them favor the Jade Wilds furnishing set due to being similar to Granny Oni's residence and how the countryside is one of Kazuha's favorite settings.
 * From the Spices of the West event, both seem to favor Fragrant Grilled Tiger Fish.