is a Japanese manga series written and illustrated by Yukinobu Hoshino. It was serialized in Kodansha's manga magazine Mr. Magazine from 1991 to 1992, with its chapters collected in two volumes.
A sequel, titled Blue World, was serialized in Kodansha's Monthly Afternoon from February 1995 to August 1997, with its chapters collected in four volumes. The story is about the discovery of a gateway in time and space deep underwater which allows for travel between the present day and the age of the dinosaurs.
Written and illustrated by Yukinobu Hoshino, Blue Hole was serialized in Kodansha's seinen manga magazine ' from 1991 to 1992. Kodansha collected its chapters in two volumes, released on August 8, 1992, and February 9, 1993.
A sequel, titled , was serialized in Kodansha's manga magazine Monthly Afternoon from February 25, 1995, to August 25, 1997. Kodansha collected its chapters in four tankà Âbon volumes, released from April 23, 1996, to April 23, 1998.