|Location||City of Aku, Underworld|
|Notable inhabitants|| Aku|
The castle acts as the place where Aku meets other Underlords for business meetings, mostly by his close friend HIM, although his meetings with HIM aren't restricted. It is often so that Mimi and Jeff come along with HIM to those meetings, mainly for Mimi and Chi to play together.
HIM visits the place without Mimi, who is at Castle of Grim, and Jeff, who is a soul now. HIM first encounters Chi who questions where Mimi is, but when not satisfied by HIM's answer shot him through his cowboy hat. Although Chi wanted to threathen him, HIM did threathened her instead. Aku then arrived, excused his daughter, and invited HIM to go to the spa.
Aku, now as Ikra, had a motherly talk with Chi about her behavior and relationship with Mimi. She understood her love but did not accept the way she was handling the situations concerning her. When Ikra went to the spa with HIM, Chi discovered her shapeshifting abilities. Not soon after she sent Demongo out to the Land of Tainted Souls to find out where Mimi is. When Demongo found Jeff and told this to Chi, she teleported to the Land of Tained Souls to let Jeff explain everything what has happened until now, while concurrently HIM told the same to Aku. Aku expressed displeasure with HIM's recent actions as he had hoped that HIM would have been more careful with Mandy, especially taking in consideration the past he shared with Mandy. He also told HIM that he had no intention to join him in his crusade against Mandy, stating that his war-waging days are over. HIM replied by stating to miss these old days and Aku has lost his zeal since the death of his adversary. He also tried to convinve Aku that helping him in this war would be in his best interest as Mandy possessed the only weapon that could kill him. Aku didn't refute this claims but told HIM that the weapon was useless in her hands, giving him no reason to wage war over it. He was willing to support HIM and stand by his side when he faces the council but that was all he was willing to do. He also told HIM that he would appreciate it greatly if he kept Chi out of this, especially since Mimi seemed already to be deeply involved.
After Chi's cat-proxy had interrogated Jeff in the Land of the Tainted Souls and got a vision of Blossom's last memories, she and Demongo returned to her room, to be absorbed by her main body once again. As soon as she received the new data, Chi started trashing the room and could control herself just enough to not harm Demongo. Instead, while lying in the midst of her trashed room, she asked him to inform her about the Grim Family, revealing her plans of infiltrating Castle of Grim.
When the Blood Council letters were send to the Underlord, HIM and Ikra were indulging in sake, slowly getting drunk in Aku's room. Ikra discussed with HIM's his plans, his future as Underlord and Mimi. Unbeknownst to them, they are spied on by one of Chi's mouse-proxies that has taken on the form of a mouse. Ikra then stated to seduce HIM, something that HIM laughs of while the proxy returned to Chi, with Ikra's last words being that HIM will have to be more persuasive. Meanwhile, Chi was bathing and when her proxy returned to her, she absorbed the proxy before deciding to leave the bath and return to her room.
Once there, she told [[her handmaidens to leave her, before entering her secret altar, which is filled with "Mimi" merchanidise. With the info, she has on both Castle of Grim and the Blood Council's plans, she planned her "rescue mission" of Mimi. At her altar, she stabbed herself in the abdomen, as a part of an experiment. Knowing her father would never let her left the castle, she made a double to fool him. Together with her doppelganger, she ate and later re-enacted the battle between Skulker and Mimi, with the necessary artistic freedoms of course before being called be her handmaidens, who inform her that her father was waiting for her, at the train platform of the castle, Ikra ordered her troops that if Chi leaves the palace, they would face her wrath. Shortly after Chi (who was in reality her doppelganger) has come to see her mother, the Cthulu Express arrived to pick up HIM and Ikra. After hugging her daughter goodbye and after some 'kind' words of HIM, both Ikra and HIM board the train.
As the train departed, the doppelganger ordered a assembly in the Castle Hall to all personell. Once all have gathered, she ordered them to dance to Gangnam Style. The real Chi observed the dance from on a balcony before leaving for the stables to get her Monochromicon, Captain Sparrow. After Demongo opened the roof, she ordered him to take place before her, before ordering her steed to go to Castle of Grim.
Meanwhile, her doppelganger is making a remake of Frozen, with Chi as Elsa in the film studio of the castle. One of the guards came to tell her that someone stole her steed. She immediately knew that it was her real self but in order to keep up the facade she ordered a search.
Aku's Castle, as well as the rest of the realm, is a metropolis city mostly consisting out of black buildings with red lights, sky and all that kind of things. However inside of Aku's castle he has taken on a Japanese culture in respect of his fallen nemesis, Samurai Jack. Everything in his home is Japanese themed.
- Aku's Office
- Castle Hall
- Castle Walls
- Chi's Room
- Film Studio
- Garden (entrance)
- Train Platform
- Aku's Room
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