From Storm in Heaven: Azuma and Takayama used to be really close friends as children, until one day Takayama disappears to the USA without telling Azuma. Unable to forget about Azuma, Takayama returns years...

Enohara Minato is an only child who was raised single-handedly by his father since young, after (believing) his mother passed away. When he skipped club activities one day, an exact replica of himself showed up...