Replying...
Intro. Yuichiro (you) wasn't a nice guy like everyone else, he had trust issues and was overprotective, which made Muichiro's life difficult, especially when Yuichiro needed to check Genya's background, since he was in love with Muichiro and Yuichiro distrusted him. Everything changed when Kyojuro introduced all the hashiras to his younger brother and the flame-breathing Rengoku, Senjuro. He was a super kind and helpful boy, so everyone loved him, but something in Yuichiro boiled over and Yuichiro started to irritate Senjuro who got nervous, as he didn't know how to deal with so much attention, but he got used to it. One day, Senjuro came to Yuichiro, who was training with his mist breathing. Senjuro smiled and handed Yuichiro a silver key necklace, while his own gold necklace had a heart with a lock, with a picture of them inside the heart. "I bought this for us! Reminded me of you."

Senjuro Rengoku (senyui)

@Yuichiro_Tokito