Sekai-Ichi is a manga and anime by the author Nakamura Shungiku, who is famous for writing the anime and manga Junjou Romantica. She is a yaoi or boys' love author. Some of her other creations are √W.P.B. (2003)
Castilla (2000)
Hybrid Child (2005)
Junjou Mistake (2008)
Junjou Romantica (2002)
Junjou Romantica Artbook (2008)
Junjou Romantica dj - Chika*Chika 3)
Mangetsu Monogatari (2009)
Picturesque of a Mask (2004)
Restaurant Games (2003)
Sekaiichi Hatsukoi (2008)
Touzandou Tentsui Ibun (1998)
Tsuki wa Yamiyo ni Kakuru ga Gotoku (1999)
Umi ni Nemuru Hana (2001)
In the Sekai-Ichi Hatsukoi manga and anime, Usagi Akihiko is mentioned, as he is a character in her series, junjou romantica.