Who's This? The Japanese superhero on page 21 of Who's Who vol.XXII.
How you could have heard of him: After Crisis, his history seems to have been pushed forward to more contemporary times, and (as per his Who's Who entry), Rising Sun replaced Superboy in those pre-Crisis stories. Grant Morrison introduced a new version of Sunburst in Doom Patrol #26 who is essentially Japan's answer to Booster Gold. He fights the Brotherhood of Dada, and may be killed doing so, but we don't know what his connection to Takeo Sato is. Sato is definitely a founding member of Big Science Action though, a Silver Age Japanese JLA seen in Final Crisis (yes, with Rising Sun).
Example story: New Adventures of Superboy #45-47 (1983) by Paul Kupperberg, Alex Saviuk and Kurt Schaffenberger
Clark is enjoying a Japanese superhero movie with his girlfriend Lisa (what, not Lana? Dude, you gotta find some New Adventures of Superboy in the quarter bin), specifically a Sunburst movie, Clark's favorite.
Who else? I think I'm ready to move on. Maybe save the Sun Devils for the second lap. I've done Super-Chief in Reign of the Supermen. And I'll be damned if I do every crappy Outsiders villain like Syonide. They ALL suck and would force me to read an Outsiders story. Who's Who vol.XXIII is on tap next.