Spoiler

Sword: Nanami's Scimitar & Dagger Drive to Duel: To become an adult.

Nanami's most devoted lackey, a boy in fourth grade. He is obsessed with serving Nanami and wishes to be her adored "big brother", even going so far as to put her in danger in order to rescue her. Tsuwabuki does not appear in the movie.

Spoiler

He becomes a Black Rose Duelist after Nanami dismisses his opinions because she considers him too young. His recurring issues with adults and adulthood are one of the show's principle themes.

(Source: Wikipedia)