Neither title is the most fondly remembered in its respective canon, though Sonic Blast has the dubious distinction of being the last game commercially released for the Game Gear in Japan. Knuckles is playable too, which is always a bonus.
The mascot duo will reach Japan on 18th April. DK Jr. will cost ¥500, while Sonic is cheaper at ¥300. Sonic Blast's been rated by the Australian Classification Board, so a release outside Japan seems likely.