Ittozou

Ittozou is the slash ship between Arataki Itto and Shikanoin Heizou from the Genshin Impact fandom.

Canon
Prior to his hangout event, as a detective working within the Tenryou Commission, Heizou mostly had passing knowledge of Arataki Itto, especially as case files such as "The Crown Prince of Mischief in Hanamizaka" based on Itto and the Gang's troublesome reputation. However, there came a point when Shinobu leveraged her connections within the Commission that saw her cross paths with Heizou, working out an arrangement where she'd give him intelligence in exchange for him looking after Itto or any of the other Arataki Gang members interred in prison.

Heizou commented that, while they'd never actually spoken, that Itto " had a good set of pipes" that referred to him being a good singer. On Itto's end, it was revealed during the "Heizou Talks Fraud" segment of his hangout quest that Itto had no knowledge of Heizou being a Doushin and thought he was a Lavender Melon seller when the detective would bring him the Oni's favorite fruit in prison; prior, he thought Heizou was in for being a sore-loser during past beetle-battles.

Trap 'Em by Storm
For the anti-fraud play that Heizou was hosting, they needed a final participant to round out the trio, and therefore selected Itto as the final player alongside Etsu and Iba. While Itto was at first enthusiastic at the idea of participating, when Heizou appeared, he became somewhat skeptical and wondered if Heizou wasn't a previous challenger he'd faced in a past Onikabuto battle that had lost to him and was seeking some sort of vengeance. However, Heizou had foresight enough to know Itto's reputation and how he loved Onikabuto, promising an Emperor Onikabuto for his participation to sweeten the deal that hooked the Oni in. At that point, he event called Hezoi his "bro, my main man, my buddy" in a similar line of dialogue from the Irodori Festival with Thoma, a trait only seen with people Itto seems to wholeheartedly approve of.

The following day, and with a stage that features art displaying both Itto and Heizou, the play itself begins with Itto ad-libbing most of his lines while Heizou narrates, creating a humorous rapport between the two that showcases a comedic dynamic. While Heizou often has to compensate for Itto's overconfidence at neglecting to learn his lines, throughout the play, it's evident that the two have good chemistry nonetheless that could be typical of a duo that falls into the brains and brawn trope. Regardless of the ending reached, the play ends on a mostly high note.

In the "Free Onikabuto Lunch" ending, Itto receives his Emperor Onikabuto, only to discover that he'd been conned and that it wasn't real, but simply a figurine that results in Itto's outrage and a humorous getaway Heizou makes with the Traveler. In the "The Three Undeceivables" ending, Itto still expresses dismay at the Emperor Onikabuto being fake, but Itto is cheered up by Heizou playing into a false story that he was conned by the Onikabuto Vendor he bought it from. Feeling much better as a result, Itto reflects on how even a smart detective like Heizou can be a victim of conmen and how the two of them grew from the experience and became a little wiser as a result.

In either ending, it either results in a memory of Itto expressing outrage at the fake Emperor Onikabuto to the mischievous escape of Heizou, or the positive ending where he chummily draped his arm over Heizou's shoulder in a show of closeness fostered between the pair.

Miscellaneous
in terms of ascension materials, both use Onikabuto. When it comes to their respective fighting styles, both are physical combatants despite Itto's reliance on a Claymore, he's often shown performing more physical melee attacks like using his super-strength and Geo Vision to obliterate boulders, walls, and even tear holes through domains. Heizou, meanwhile, combines his Catalyst with physical combat to augment with Anemo to perform devastating kicks and punches reminiscent of some of Itto's attacks.

In contrast to their superior (Kujou Sara) and subordinate (Kuki Shinobu), respectively, both men have an extremely laid back approach to their chosen vocations. While Itto is a firm believer in a day of work followed by three days to slack off, Heizou is extremely atypical for a Doushin and neglects the majority of his duties except the most important, which relate to solving cases he personally finds interesting. Both have an unorthodox but independent approach to life and appreciate a high degree of freedom.

Throughout Heizou's hangout event, the pair commonly referred to each other as "bro."

Quotes
"I've done a few favors before to deliver Roasted Lavender Melon to him in prison. This one time, I overheard him singing. The lyrics... were complete trash, but I gotta say — he has a pretty good set of pipes. And it's not every day you come across an inmate who's in the mood to sing their heart out."

- Shikanoin Heizou, About: Arataki Itto

"Several times now, I've been sitting there, starving in jail, when this guy comes and slips me a few Lavender Melons on the sly. Didn't even want payment. Solid guy!"

- Arataki Itto, Heizou Talks Fraud

"But you'd better watch out. We got fooled, not because we were stupid, but because those scam artists are some crafty dastards! I want you to have this figurine, as a reminder of the fact that today, Heizou and I both got conned, but we both grew a little wiser, too. I hope that whenever you see it, you'll remember how cunning those con artists were, and how difficult it was for Heizou and I to see through their schemes. Then, you'll always keep your wits about you, and you'll never become a victim yourself."

- Arataki Itto, Heizou Talks Fraud

Fanon
Currently, because of the newness of the ship, there isn't a great amount of content for this pairing, with roughly over 28 works on AO3 and a negligible amount of works yet to emerge on the pairing. Because of how recent Version 2.8 was and of the other content released, it's likely that the ship will experience growth with time. Currently, the ship sees rivals in pairings like IttoGorou on Itto's end and Heikazu on Heizou's.

Regardless, both still follow some classic tropes, such as Itto being the bad boy while Heizou is the one who upholds the law. Despite this, however, they seem to flip even that on its head with Heizou rarely pursuing petty cases that Itto's misbehaving seems to fall under while presumably having the upper hand on any interactions of theirs. Heizou is also more secretive with his intentions and even body language while Itto is commonly cited as being overemotional and extremely easy to read, making them a case of 'opposites attracting'.

Due to Heizou's high intelligence and Itto's lack thereof, they nonetheless share values in personal freedom and helping people out, however unorthodox their methods may be.

Fandom
FAN FICTION

Trivia

 * Both use Onikabuto in their ascension materials and are the only two characters that do.
 * The stage used for the "Heizou Talks Fraud" play featured art of both Heizou and Itto.