I-No (/ˈiːnoʊ/ ^ⓘ EE-no; Japanese: イノ, romanized: Ino) is a character in Arc System Works' Guilty Gear fighting game series. Created by Daisuke Ishiwatari and first appearing in the 2002 video game Guilty Gear X2, she was originally conceived as a replacement for previous character Justice in the title, and a combination of a wizard and a musician. Ishiwatari designed her to be "the ultimate erotic character", making her cruel and sexually aggressive, while basing her physical appearance on musician Ringo Sheena. In the game's setting, she is a minion of series villain Asuka R. Kreutz, though works towards her own goals, and often manipulates the other fighters against each other. Since her initial appearance, she has since gone on to appear as a playable character in most Guilty Gear series titles, as well as several mobile games. She is voiced in Japanese by Kikuko Inoue, and by Amber Lee Connors in the English localization of Guilty Gear Strive.

I-No has been praised for both her character's sex appeal, but also her high difficulty as a boss in Guilty Gear X2. Called one of the fighting game genre's "most magnetic fighters" by Destructoid, approval from media outlets also came in regards to her character and how she emphasized "evil as sexy", and fit the image of a "rock and roll lifestyle". Though some complained that she was often shown being defeated in the game's story, her presence as a manipulator working towards her own goals and the twists with her character also saw praise. Meanwhile fan reactions to her were seen as breathing life into the character, and that her counter-compliant nature provided her with an illusion of agency.

Created for Guilty Gear X2, I-No stands 5 ft 5 in (165 cm) tall. I-No has a black hair in a bobcut, and wear fingerless black gloves, red thigh-high platform boots, and a choker. Her body is covered in a black and red tube dress that stops just below her breasts, while her jacket exposes her shoulders and strips of cloth dangling from it over her chest. The jacket is connected to fabric around her neck with a ring extending from it, which she can use to remove said jacket quickly. She has a witch's hat stylized after a skull, with a "mouth" she can animate to fire projectiles in some of her attacks. Her primary weapon is "Marlene", a blue guitar modeled after the Duesenberg Starplayer. In terms of personality, I-No is described as completely self-centered, and due to this sees others as just livestock able to be sacrificed. Due to her abilities she lacks empathy, though tries to keep her nature hidden unless she loses her composure.

In each installment of the series her outfit remained consistent until her appearance in Guilty Gear Strive, in which it was changed entirely. While the red witch's hat, black gloves, choker, thigh-high boots and blue guitar remained, her dress was replaced with short shorts, and a belt atop them that featured coat tails hanging off it. Meanwhile her midriff was now exposed, with her torso covered by a black unbuttoned shirt that cups her breasts, and a cropped red leather jacket. The brim of her hat was expanded, and she now wears green sunglasses. Regarding the design change, Ishiwatari stated it was to take into account global audiences, not wanting it to be seen as due to "regulations" but instead a "change in expression" to "allow more users to play the game".

In all appearances, I-No is voiced by Kikuko Inoue in Japanese, and in Guilty Gear Strive by Amber Lee Connors in English. Much of I-No's dialogue is cruel and sexually charged, with the developers intending such to not only shock men and women alike but be captivating as well due to her portrayal as an evil woman. However, as a boss her dialogue changes to a significantly more aggressive tone. According to Inoue "She is the scariest role I’ve ever played. I’ve never said such abusive words before, and I’ll probably never have a chance to say them again." However, she also wanted to express I-No as strong, due to her doing evil for her own sake rather than a reason such as revenge. Connors meanwhile stated she was a huge fan of the character's design, and during the audition period Arc System Works requested two takes, one attempting to match Inoue's tone and another with Connors' own approach to I-No's voice. The company went with the latter upon hiring her, which Connors referred to as a "dommy mommy" take on the character.

When developing X2, they originally considered bringing back the character Justice, the final boss from the original Guilty Gear, as a playable character. Series creator Daisuke Ishiwatari however wanted instead to explore a new character that was based on several aspects of Justice, feeling that simply bringing Justice back would diminish some of their impact. When developing I-No, he gave her a "wizard-like" silhouette, while wanting to push the "limits of eroticism" with her design. He emphasized this in particular with how he drew her guitar, aiming to avoid making it feel like attacking with a baseball bat and instead appear erotic in motion, trying to plan out movements that felt interesting to watch. He wanted her color scheme to be a departure from that seen with previous Guilty Gear characters, giving her overall appearance, and heavily detailed her guitar. When project manager and animator Toshimichi Mori suggested just drawing the guitar as glossy, Ishiwatari refused and insisted that "Whatever it takes, draw it in every detail!"

While the concept originally started as a wizard, they felt the design would be too plain for Guilty Gear universe. It was considered to give her a large iron club, before deciding to make her look like a "delinquent". Going with a combination of a wizard and a musician, Ishiwatari stated it changed as he added his own tastes, wanting to portray someone that was "absolutely evil", but also the "ultimate erotic character". To complete the aesthetic, her guitar was meant to take the place of a witch's broom, allowing her to fly while straddling it. His concept art focused focused not only on heavily detailing her props such as her hat and guitar, but also the shape of her breasts under her jacket and her underwear, with several pieces depicting her near nude. Her name was inspired by musician Brian Eno, while physically she was based on musician Ringo Sheena. Ishiwatari stated the similarity was not originally intentional, and came about due to modelling her after "the most feminine person" he knew, even giving I-No a beauty mark in the same position as Sheena's. He noted that when coming up with the design, he even considered asking her to provide the character's voice. A key element Ishiwatari had in his mind regarding her character was "the fear of women from my perspective", and when illustrating her tried to maintain that image by changing her characteristics in various ways. In-game, I-No is often portrayed in "lewd situations" according to Ishiwatari, something he felt was a key part of her character.

As introduced in Guilty Gear X2, I-No is a playable character, while also serving as the game's antagonist and final boss. She works under series villain Asuka R. Kreutz, though of her own accord due to wanting to see what happens when his plans come to fruition. To this end she tries to eliminate anyone that can impede his goals, particularly manipulating the other characters against each other to this end. Able to manipulate time and causality, in Guilty Gear Xrd it's revealed she is actually the culmination of humanity's "hopes and desires" for a better future, with half of her power having been stolen by villain Happy Chaos. After this revelation, I-No becomes obsessed with finding the answer to her purpose in Guilty Gear Strive. However even after recovering her power she is unable to, and tries to pass her abilities onto all of humanity so they might be able to in the future, despite the consequences. The protagonists fight her, and in the ensuing battle her body destroyed.