Get to know Aguni!

As demonstrated during various Spades games, Aguni is perceptive and calm, he excels at working out his opponents' strengths and weaknesses to be able to come up with a successful strategy. Despite the circumstances, he never shows fear and never panics, turning all his emotions into rage and using them to defeat the enemy. However, when left alone with his pain, he sometimes allows himself to let it out, such as when he cries after killing Hatter or when Arisu sees through his angry facade and notices his grief.

Murdering Hatter deeply traumatizes Aguni, he turns his pain and guilt into the decision to kill all the Beach members, blaming them for driving his friend insane, and then keeps hallucinating of Hatter judging his actions. 

As stated by Aguni himself, he trusts in his friends, which is all the hope he needs in life, however, after it ends up being not enough to save Takeru, Aguni shuts his feelings down and decides not to trust people any longer, which results in the strange dynamics between him and Heiya, whom he teaches to be better at strategy and fighting, but whom he cannot let closer despite her obvious romantic interest in him.

History

Aguni's backstory is mostly intertwined with Hatter's, as they are shown to be close friends in the real world before the events of the series. After Takeru took over his father's "Hat Danma" shop, Aguni came to visit him and tried on one of the hats, but Takeru stated that it did not suit him. He commented on Aguni becoming an SDF officer and joked that he had expected him to belong to the yakuza. Aguni mentioned another mutual friend of theirs who had been killed, and Takeru told him to live a long life as he was the only friend he had left. Aguni smiled and wished Takeru the same.

After arriving in the Borderlands, Aguni and Hatter cleared multiple games before discovering the Seaside Paradise Tokyo hotel, where Hatter decided to create a utopia. Aguni was skeptical of the idea but agreed to support his friend's dreams and took on the role of the militant leader in charge of weapons and security.