Yu Nogi

Yu Nogi (乃木 優) also known as K, is the best friend of Keisuke Amasawa and a talented hacker that stole the avatar of Keisuke to fulfill his longing to be with Keisuke.

Appearance
Yu is an effeminate looking young man with medium length purple hair, purple eyes, and fair skin. He commonly wears a purple hoodie over a black shirt and white pants.

While under the guise of "K" he wears a mask that obscures his face along with a multi colored jacket, red pants, and white shoes. The mask he wears however is possessed by a Matadormon whose giving him the prowess in hacking and fanatically controls him in story progress.

Etymologies

 * Yu Nogi

Name used in Digimon Story: Cyber Sleuth - Hacker's Memory.
 * K
 * , after Keisuke.

Fiction
Yu is Keisuke Amasawa childhood, and only, friend and have known each other for over 10 years. Yu is in love with Keisuke but Keisuke does not return these feelings. This leads Yu to becoming an evil hacker known as K.

K is a mysterious hacker who contacts Keisuke with information on hackers that account raid, in an attempt to find out who stole Keisuke's account. Keisuke follows these leads, though eventually joins hacker team Hudie and Ryuji Mishima attempts to force Keisuke to cut contact with K. Keisuke ignores Ryuji and continues to follow the leads provided by K, which leads him to defeat Youji Shiga and Tooru Kayaba, though neither are shown to have stolen the account. Eventually, he gives a lead on Akira Hosaka, which leads Keisuke and Yu, who "happened to be there" when K contacted Keisuke, to fight Akira. Upon defeating him, Akira reveals he did indeed steal Keisuke's account but found the account so boring, he sold it off a long time ago. Before Keisuke can get any more information out of him, Yu deletes his account, removing his only lead on his missing account.

After this, Ryuji is angry at Keisuke ignoring his warnings on K and demands to come with him the next time they plan to meet up. Keisuke plans a meeting with K who reveals he has now taken over leadership of Demons, though whilst discussing other hacking targets, Ryuji comes out to confront K. K is annoyed Keisuke didn't come alone, so sends out five Digimon to fight the two, whilst escaping. Later, Keisuke confronts K on his own, who then locks Keisuke away in an electrified cage and states he will let him out "eventually". He then takes off his mask, revealing he had been using Keisuke's account all along and that Keisuke is an impostor with K being the real Keisuke. After leaving, Wormmon suddenly appears on Keisuke's back and reveals Erika Mishima had forced him to come along in secret, as she didn't trust him to go alone. Wormmon claims he will help Keisuke out, though after pointing out that both of them are locked in the cage, Wormmon panics. Erika then contacts Keisuke and chastises him for trying to go out on his own again, then after Keisuke apologises, hacks the cage and allows the two two escape.

Keisuke then returns to the real world and manage to track down K, who is causing havoc in the streets with his SkullSatamon. K expresses shock that Keisuke had managed to get out the cage, then takes his mask off yet again, showing that he is now Keisuke in the real world as well, as using the account in Eden caused his appearance to change in the real world to match his stolen account. With no need for two Keisukes, K orders SkullSatamon to attack and kill the defenceless Keisuke, who's Digimon had yet to realise in the real world, unlike K's, and other, Digimon. Just as SkullSatamon was about to kill Keisuke though, Keisuke's Digimon appear out of his Digivice and protect him from the attack. This doesn't last very long however, as SkullSatamon easily defeats all of Keisuke's Digimon. Just before SkullSatamon can kill Keisuke though, Ryuji and Arcadiamon arrive, with the Rookie level Digimon easily defeating SkullSatamon and then absorbing it. Arcadiamon was about to absorb the defenceless K too, though he manages to escape.

Keisuke and Wormmon then return to the Demon's Den and find a link to a server, known as "K's server". Whilst transversing the area, memory fragments play in Keisuke's mind, revealing a dark aura had been talking a K for a long time, convincing K to steal Keisuke's account to get closer to him. These memories reveal that K was actually Yu Nogi and that he worked together with Akira Hosaka to steal accounts, then personally requested Akira stolen the account of Keisuke. Upon doing so, K then turned on Akira and stole his account, as well as access to every account Akira has stolen up to that point. He then posed as Shiga, Kayaba and Hosaka, whilst sending Keisuke on an endless wild goose chase. Each time Keisuke would come up short, Yu would play the support role, cheering him on from the sidelines whist "warning him not to get into trouble" and when Keisuke would eventually get his account back "thanks to Yu", he would "fall in love Yu" due to how good a friend he had been. This plan however, didn't play out the way Yu wanted, as whenever Keisuke ran into trouble during his attempts to get his account back, he would instead rely on his friends in Hudie and not Yu, like Yu wanted. This enraged Yu, leading the aura to suggest Yu himself become Keisuke, which lead to the events of Yu trying to murder the one he was in love with. Upon Keisuke reaching the end of the server, K removes his mask, revealing he was Yu all along. When Yu begs for forgiveness, the mask transforms into a Matadormon, who reveals he had been manipulating Yu the entire time and mocks Yu for failing in his goal to have Keisuke fall in love with him, revealing multiple secrets whilst doing so. Keisuke defeats Matdormon, who then turns back into a mask and Yu discards it once and for all, though Matadormon ends up in the Abyss Server as a GranDracmon. Keisuke forgives Yu, which shocks Yu. Yu proceeded to ignore Keisuke, until Keisuke needs helps hacking into Eden when the servers are down. Yu hacks, allowing Keisuke access to Eden and states he did so to try and make amends.

After the world is reset due to Aiba defeating the Mother Eater and with Erika Mishima being erased out of existence in the human world, as well as Digimon no longer arriving in the human world, meaning Matadormon was unable to manipulate him into being evil, Yu becomes an official member of Hudie, alongside Keisuke in the new alternate universe, taking Erika's place.