Note that in Japanese, the number 3 reads 'mi' and 7 reads 'na', so 373 = Minami. 
Izumi is nervous before a championship game, so Koji makes him feel better with graphic fluidy sex in the shower. Izumi goes on to the game (with Wakashimazu and Hyuga as team mates) and kicks soccer butt. (Source: zetsuai.org)

When he was very young, his mother killed his father and also hurt him badly; that may be the reason why Takuto Izumi, high school soccer star and the girls' idol, is so cold towards other people. He trusts no-one, and refuses to love anyone, so he leaves his adoptive family and goes to live on his own as soon as he's capable.
 
As he's struggling to put the past behind him, a certain incident on a dull rainy day turns his life around completely. The drunk he helped out on a whim turns out to be the famous idol popstar Nanjou Kouji, and ever since that encounter, Kouji has taken an interest in Izumi... An interest that seems to grow deeper every day until it becomes what can only be described as "obsessive love."

The story picks up after Zetsuai 1989, Koji and Izumi as a couple.  Izumi decides to leave for Italy for soccer, Koji races to meet him at the airport getting into an accident.  Now, Koji, a famous rock star,  cannot sing after his accident.  Will Koji and Izumi ever come to terms?

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