SEGA has already released several 3DS themes promoting its recently released SEGA Archives (aka 3D Classics) in Japan, and they have a few more now available in the Japanese eShop.
A Space Harrier and Fantasy Zone theme have been released today for 200 yen each.
SEGA has previously released a Mega Drive anniversary theme, an Astro City arcade cabinet theme, a Sonic the Hedgehog theme and Puyo Puyo theme.
You can visit the theme pages for Fantasy Zone here and Space Harrier here.