Decipher the Past

Hiro Hamada had tried to move on from his brother's death in the past two years and so far it worked. Until, one day, a new customer to Aunt Cass's cafe turned Hiro's world upside down, especially when the said customer looked exactly like Tadashi, even his name. Tadashi Takachiho-who is he? [Hiro/Tadashi deep brotherly. No incest here.]