I-No is a major character in the Guilty Gear series. She is a time-traveling musician who seems to derive pleasure from tormenting others, and is one of That Man's three servants alongside Raven and Jack-O' Valentine. Very little is known about her, with a report in Guilty Gear XX that consists entirely of "UNKNOWN!!" repeated several times over.

Initially unveiled at EVO 2022, a music video to commemorate the 1st Anniversary of "GUILTY GEAR -STRIVE-", animated by studio SANZIGEN. The video, directed by Shinpei Ishikawa, features the theme song Find Your One Way of the main character of the series: Sol Badguy. This music video depicts more than 20 years of the world of Guilty Gear and half his lifetime!
 
(Source: Arc System Works Twitter, edited)

Mahiro Oyama was just a normal erotic-game loving dude…until he woke up one morning as a woman! Turns out his mad-scientist little sister, Mihari, tried out one of her new experiments on him…with a disastrous outcome, as far as Mahiro’s concerned! But Mihari is as determined to study him as he is determined to go back to his shut-in, game-playing life, and one thing’s for sure…life is going to get a whole lot weirder from here on out! 
 
(Source: Kodansha USA)