Boss is actually Cupid, an angel of love who has a mission to make Modem and Light fall in love with each other.  However, He falls in love with Modem at first sight and fails to accomplish his mission.  Cupid tries to negotiate with Heaven that if he can make Modem fall in love with him, they can be together forever.  But when Modem meets Light again she knows who she really has feelings for.  After that, Light asks Modem to meet at their old school but Cupid uses the love potion to make Modem fall in love with him. 

Boss asks Modem to be his girlfriend.  She says yes but can't stop crying.  Boss then realizes that he's not the one for her and lets her go.  Modem follows Light trying to talk everything out with him.  Although Light doesn't listen, Modem is still persistent.  She tells him all the truth in her heart.  THen, the two reconcile and start dating.  Meanwhile, Boss comes to say goodbye to Modem but he ends up leaving without doing so.