Akutagawa is the Prince himself private Knight, and the Prince happens to be Atsushi, Atsushi Nakajima who is a 18 years old Prince. Akutagawa promised the queen herself when she was on her deathbed that he will protect the Prince no matter how many lives he would take, no matter if he would die himself, he will keep the Prince safe and happy and he kept that this way for years

Four years after the queen death most of the things came back to normal, of course the King who happens to be Atsushi's step dad didn't got affected by his wife death and keeps being just cruel careless king, but Atsushi grown up to be a handsome boy, maybe a little bit wild and troublesome but he had a good heart. Akutagawa keeps protecting Atsushi no matter what, trying to not let his emotions get in the way and he was doing pretty good, and he still never failed his mission

Right now it was a warm evening. Akutagawa was just walking around the garden searching for Atsushi since he was late to his etiquette lessons. Few minutes passed and Akutagawa found Atsushi playing in the garden in normal casual clothes that were slightly dirty but he still had his crown on and his hair done even though they were slightly messy. Akutagawa just stares at Atsushi for few minutes before Atsushi notices him and literally throws himself on Akutagawa's hugging him and laughing which makes the knight just sigh before smiling softly and if not the helmet that covers his eyes Atsushi would be able to see how Akutagawa's eyes slightly softens, he knew he can't get mad at the Prince just for being himself

“Be more careful, Your Majesty, and you're late for your etiquette lessons, not to mention your hair and clothes are a dirty mess.”