Pluton Ainzach is the Guildmaster of the Adventurer's Guild in the city of E-Rantel. He is a middle-aged man who presents a mighty and majestic appearance, with well-kept hair and a trimmed, smooth mustache. His clothes are clean and reflect his former success as an adventurer and his current position of status. Although his skin and muscles suggest he is a man in his early forties, his hair has grayed considerably, a clear sign of the stress from numerous dangerous quests he has undertaken, indicating he has witnessed terrifying things but emerged stronger and wiser.

Ainzach is a capable and vigorous individual, exuding the atmosphere of a veteran who has faced a hundred battles. By human standards, he is considered an outstanding warrior. He has a pragmatic side, shown when he wished to keep the adamantite adventurer team Darkness in E-Rantel by any necessary means, including gaining the mayor's support to plan a welcoming banquet with offers of women, alcohol, and power. He is married.

In his younger days as an adventurer, Ainzach captured undead monsters from the Katze Plains and delivered them to the Imperial Arena in the Baharuth Empire. Over time, he rose to become the Guildmaster of the E-Rantel Adventurer's Guild. In this capacity, he assembled the city's mithril-ranked adventurer teams to discuss threats such as the powerful vampire Honyopenyoko. He also requested Momon, the leader of Darkness, to search for a rare herb and later attempted to assign other teams to assist him, only to be shocked when Momon revealed the quest was already complete.

Following the ceding of E-Rantel to the Sorcerer Kingdom, Ainzach was one of the few people who chose to stay behind. The Sorcerer King, Ainz, visited him to discuss the future of the guild. Ainzach was surprised by the proposal to offer full support to the Adventurer's Guild, with the goal of sending them to explore unknown lands and become true adventurers again. This vision resonated with the retired adventurer, and he agreed to cooperate. He began to act alongside Ainz in adventurer-related matters, providing valuable advice based on his extensive experience. During these interactions, Ainz found Ainzach's perspective refreshing, as he was not an NPC who would blindly agree; on occasion, he would deny or retort Ainz's words, which moved the undead king internally.

Ainzach became a key advisor and companion to Ainz during a secret trip to the Imperial Capital. His extensive knowledge of the adventurer's lifestyle and mindset was the primary reason for his inclusion. He helped arrange a meeting with a fight promoter named Osk and suggested that Ainz himself fight in the coliseum as a way to advertise a recruitment plan for new adventurers. When Ainz gifted him a high-quality short sword from the game YGGDRASIL, Ainzach was humbled and promised to help with all his strength to repay the kindness. He was present before Ainz's match against the Warrior King, asking if he would be alright, and Ainz assured him of his victory.

While Ainzach initially shows nervousness and deference when in the presence of powerful beings like the Floor Guardian Albedo, he also has a sense of pride. He took offense when Albedo referred to him as a worker, emphasizing his position as a guildmaster. His primary motivation becomes the revitalization of the Adventurer's Guild under the new order of the Sorcerer Kingdom, as he sees an opportunity for adventurers to move beyond simple security work and embark on true exploration. Throughout his appearances, Ainzach demonstrates himself to be a competent, wise, and energetic leader who is open to change and becomes a trusted, if initially cautious, ally to Ainz Ooal Gown.