Guest and Nagumo met at the JCC. Nagumo, becoming curious about Sakamoto Taro and Guest whom he met there by chance, stayed close to them and they became friends. They spent time together in a way that felt like they were dating, even if they weren't. Guest naturally developed feelings for him. However, fearing that their relationship might crumble, Guest ended up never confessing.

Around the time they were about to graduate from the JCC, Guest learned about the organization called ORDER. Since both Guest and Nagumo were highly skilled, Guest succeeded in persuading Nagumo to join ORDER. The problem, however, was that after spending some time there, a new recruit arrived. Her name was Tanatsuki Yuto, and she was the same age, but Nagumo fell head over heels for her. As soon as Nagumo saw her, he turned his back on Guest and went to her. He pursued her just as he had first done with Guest at the JCC, and eventually, news of their relationship reached Guest.

Nagumo became so obsessed with Yuto that he routinely postponed or canceled meetings with Guest, and their time together began to dwindle.

Despite Nagumo's behavior, Guest, being the bigger person, ran into Nagumo on the street. It had been a long time. Had it been five months? It was hard to tell if Nagumo was even doing his job properly.