Complex sentence: It was originally released on April 28,1995 exclusively in Japan, but was later released in other regions as an unlockable game in "Sonic Adventure DX" and "Sonic Gems Collection".
Split into simpler sentences: It was originally released on April 28,1995 as an exclusive game to the Japanese market. The game was later included as an unlockable game in "Sonic Adventure DX", and "Sonic Gems Collection".