Kosuke Kisakata

Kosuke Kisakata is the leader of the Sons of Chaos and is a legendary hacker. He is known by the name Tartarus (タルタロス). Very few people know his actual name and he usually uses fake accounts to hide his identity. His partner is.

Etymologies
Name used in Digimon Seekers.
 * Kosuke Kisakata

Digimon Seekers
Though Kosuke sets up the SoC's missions, he rarely gets involved himself.

He is obsessed with BlackAgumon, and has put up a mission with a 1 million DC reward for anyone that can get him one.

When Eiji applies to join the the SoC, Tartarus does an interview with him (Eiji unaware of this fact, as Tartarus was using a generic account). Tartarus tells him that he can only join if he is a good code cracker, to which Eiji asks if he is whether that would allow him to meet Tartarus. Tartarus finds this curious, though Eiji insists that since Tartarus is so well known anyone would want to meet them. Tartarus tells him that if he is really good, one of the higher ups would eventually contact him and allow him to meet Tartarus but that very few members had actually managed to meet him. Tartarus sends Eiji an exam, and tells him to complete it. Eiji finds that the mission is named "A Wolf at the Back Gate", which he finds odd since he has, though doesn't mention that fact. Tartarus tells him that nine out of ten people who do the exam lose their Digimon, and they would not insure his Digimon for him or pay compensation should he lose his Digimon. Eiji wasn't deterred though and proceeds to Mindlink.

Tartarus waits for Eiji on top of a building whilst Mindlinked to, who hides under a cloak to hide its identity. Eiji, Mindlinked within Loogamon, arrives two minutes late which causes Tartarus to dock him two points on the mission. Eiji suddenly appears next to Loogamon, which surprises even Loogamon. Eiji explains he had remembered he was told he could access commands on virtual monitors by thinking of doing it and having seen a button saying hololize simply thought of pressing it which allowed him to hololize next to Loogamon. Tartarus was also surprised and tells Eiji that his mission is to create a map of Ninth Avenue for them, and that he just has to walk around the area with the provided map tool as it would auto fill the information for him. Loogamon laughs, and informs Eiji that the mission was perfect as it had something it needed to do in Ninth Avenue anyway. Tartarus wishes Eiji luck on his mission, hoping he would be able to pass and become a member of the group.

As they watch Eiji and Loogamon leave, Dorumon tells Tartarus it was surprised Eiji was also Mindlinking to which Tartarus expresses surprise at not just that but the fact that Eiji had already shown up with his limits unlocked. It wonders if Loogamon had noticed they were also using Mindlink then asks why Tartarus had given the Demon Wolf of the Castle of Nine Wolves such an easy mission. The SoC member realizes Dorumon was right and contacts the DigiPolice, telling there where Eiji was.

When Eiji and Loogamon arrive at the Castle of Nine Wolves they are intercepted by the DigiPolice who ask to talk to him on GriMM. Turning down the request would be seen as going against the DigiPolice but Eiji had no choice in the matter as his means of communication during the mission was in the hands of Tartarus who proceeds to turn down the request.

Dorumon and Tartarus, still Mindlinked, watch in awe as Eiji and defeat the DigiPolice. After the two of them leave, Dorumon chastises Tartarus for telling the DigiPolice about Eiji, though he just muses that he was right about how powerful Loogamon was. He notices that Eiji had completed the mission having sent him the map data, and decides to accept him as an official member of the Sons of Chaos in the hopes that Eiji will be able to lead Loogamon into become an even more powerful Digimon. The wind then blows off Dorumon's cloak.

The members of Operation Infinity meet up in Marvin's SoC GrimM room, with there being eight users there total. The monitor displays the mission, which is to hack X Nation's server. Hackers from X Nation had performed lots of cyberattacks and had even recently stolen billions worth of cryptocurrency. Since the SoC use cryptocurrency they couldn't turn a blind eye to them doing such a thing, especially if it caused a major shift in the World's financial powers. The SoC plan to destabilise X Nation's leader as well as get revenge on them, as they had done crimes using a Machinedramon and framed the SoC. Tartarus arrives, introduces himself as the leader of the SoC to the new members, and then tells them to render their server useless and capture their Machinedramon.

The SoC's plan to get revenge on X Nation for framing them for crimes they didn't commit by hacking into their servers and stealing their Machinedramon ends in failure after Leon Alexander and defeat them, and also kill the Machinedramon. Shortly after the failed mission Dorumon and the Hololized Tartarus, who was using his interviewer account, visit Marvin Jackson is in his room in the Sons of Chaos GrimM channel. Dorumon asks how was, with Marvin stating that it was okay but would be out of action for a while due to the injuries it had sustained at the hands of Kazuchimon. He tells Dorumon that Eiji, the hacker that Tartarus had personally scouted, had saved him and wonders if he should retire having lost that badly. Social media had become ablaze with rumours about how Judge had single handedly defeated the SoC, with the SoC themselves having leaked this information. Dorumon and Tartarus tell Marvin they would not let Judge get away with it and would get revenge against him as he poses a threat against not just the SoC but the entire Crack Team. Marvin asks if the duo are going to go ahead with their plan for an all out war, with them confirming that even with the loss of Machinedramon the final piece of the puzzle had still fallen into place. They discuss Eiji and Loogamon, saying that they had only seem him digivolve to Champion and as such didn't know whether they could trust them to stick with them till the bitter end without seeing their full power. He asks Marvin if he is still dedicated seeing Tartarus's plan to the end, to which Marvin confirms he is.

Tartarus sends Eiji a message, praising him for his work during the attack on X Nation's server with Tartarus stating he wants to hire Eiji again in the future. He asks Eiji to get revenge against Judge for interrupting their mission since failing to retaliate would lower the image of the SoC. He allows Eiji to determine Leon's punishment, with Eiji stating he would only do so under those conditions. He comes to the agreement that if he could get Leon to agree to never interfere with the SoC again, they'd let him get away with just an apology. He otherwise, would have to take Leon out. Eiji is unable to come to an agreement with him, leading to a battle in which Leon overuses his Mindlink causing him to become DMIA and fall into a coma. Presumably unaware that of the  had shown up in the middle of their battle and Leon had sacrificed himself to save Eiji from it Tartarus sends Eiji a message congratulating him on taking out Leon, telling him he was the hero of the Sons of Chaos.