Active primarily as a child actor in the 1980s, Tatsumi earned high praise for his roles as Takayuki Yoshizawa (Dankichi) in the film MacArthur's Children and as the protagonist in his younger days in Itoshiki Hibi Yo. He then garnered significant attention for voicing the protagonist Seita in the 1988 film Grave of the Fireflies. He was 16 years old when he voiced Seita in the film, partly because Seita's character was 14—an age close to Tatsumi's own at the time—and partly because the story is set in the Kansai region, where he was from; director Isao Takahata had also specifically sought out actors from the Kansai area. He later remarked, "It's easier to empathize when the character is close to your own age," and this was also the case with Ayano Shiraishi, who voiced Setsuko.
In the movie pamphlet, Tatsumi remarked, "I think if he had been more articulate, he might have had an easier life," and "Since things get harder as life goes on, I think if he could have apologized more honestly, he might have managed to live a better life." When the film was first broadcast on Friday Roadshow, he stated, "I don't think I'd want to live a life like Seita's." On Setsuko, he drew a parallel with his own tendency to be cold toward his own younger brother, saying, "I don't think I could be that kind." As for Shiraishi, he remarked, "Her voice made it much easier for me. Because it was her voice, perhaps that's why my lines came out so naturally when Setsuko was on the verge of death at the end."
Since Tatsumi's appearance in the TV drama Buchō Keiji (aired June 24, 1989), no further entertainment activities have been confirmed, and his current whereabouts are completely unknown. When a commemorative event for the Blu-ray release of Grave of the Fireflies was held in 2012, the organizers reportedly made every effort to invite Tatsumi, but were forced to give up because they could not find his contact information. Since the event was livestreamed online that day, he was even urged to "come to the venue if you're watching," but this did not come to pass.[2]