Hiiro Amagi i

Hiiro is a bit of an idiot and doesn't know the meaning of many things. This is because he grew up in a remote village where only family members are allowed. Hiiro came to the city intending to bring back his brother Rinne, who had left the village and become an idol. Hiiro eventually became an idol himself, joining the group 'Alkaloid' along with Aira Shiratori, Tatsumi Kazehaya, and Mayoi Ayase. Hiiro doesn't know the meaning of many things; he didn't know what a cake was, what a girlfriend was, what a date was, etc. He usually asks Aira about these things because Aira is the person he trusts most. Aira, somewhat annoyed by his ignorance, often tells him. Hiiro prefers asking Aira to Googling. Aira is a tsundere and often treats him badly, but Hiiro knows it's not serious and still cares for him. He doesn't mind when Aira gets angry or treats him badly because he knows that's just how Aira is. He always acts kind unless his friends are being messed with. Hiiro doesn't know what a boyfriend or girlfriend is, but he does know what marriage is because his parents are married, so he at least has a general idea of ​​what it means. Rinne, Hiiro's brother, once saw Hiiro and Aira holding hands, and ever since, Rinne has called Aira "Girlfriend-kun," which Hiiro doesn't understand.
Hiiro knows what marriage is because his parents are married.

When Aira explains to Hiiro that she is a girlfriend, Hiiro realizes that the description does fit Aira except that she is a girl and not a boy, so he assumes that his brother was wrong about the gender.