REBORN! - Season 4 Episode 78

While recovering from his injuries, Tsuna learns the only way to return to the past is to gather the guardians, defeat Byakuran and eliminate the man with the glasses, Shoichi Irie. Lal-Mirch teaches Tsuna, Yamamto, and Gokudera about the rings and boxes; The rings are revealed to emit a flame depending on the element of the user and boxes contain weapons or animals enchanted by those flames. Lal Mirch asks Tsuna to open a box of an unknown element as the sky flame is able to open boxes of all elements.