Her television credits include the English versions of several 1960s-1990s Japanese series such as Marine Boy (voicing Marine Boy as well as Neptina and Cli-Cli), Star Blazers (voicing Mariposa and Nova in the third season), Ultraman and Ultraman Tiga.
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.
Ultraman | Ultraman Tiga | Tiga Dam | Pulau Tiga National Park | Ultraman Zero: The Revenge of Belial | Ultraman Nexus | Ultraman Gaia | Ultraman Cosmos vs. Ultraman Justice: The Final Battle | Ultraman Cosmos | Ultraman Ace | Ultraman 80 | Madu Tiga | A scene from the original flash animation for "Okkusenman!" featuring the subject of the song as an adult while a caricature of ''Ultraman |
As part of a Kodomo no Hi report, the Oricon listed "Engine Sentai Go-onger" as the #1 tokusatsu hero karaoke request, ahead of songs such as AAA DEN-O form's "Climax Jump" for Kamen Rider Den-O and V6's "TAKE ME HIGHER" for Ultraman Tiga.
In the mid-1990s, he joined Tsuburaya Productions, the creators of the popular Ultra Series, working as an Assistant Director on TV series such as Ultraman Tiga.