Ultraman Tiga
Hasegawa began writing for television in the 1990s and has been a writer for almost every "Ultraman" series produced since Tiga up to the first season of Ginga. Since first beginning his work on the Ultraman franchise with the 1996 series "Ultraman Tiga", Hasegawa has gone on to write more material for the franchise than any other writer. He has been directly involved with the creation of every title Ultraman character up to Mebius as well as having had a major role in selecting actors for the roles.