Dragon's Flag

(from ebookjapan):

Blue skies, white waves, uninhabited islands. Ryoma Mori is a boy who dreams of leading the world's largest fleet of boats on an endless adventure across the seven seas.

When Ryoma is welcomed by all the teachers and students at his new school, he is immediately confronted by a group of bancho. What is the meaning of the Dragon Flag that Ryoma, a sergeant of the Mori family, a large Brazilian conglomerate, holds dear?