Sonic the Hedgehog CD

Sonic the Hedgehog CD (ソニック・ザ・ヘッジホッグCD, Sonikku za Hejjihoggu Shī Dī), or Sonic CD (ソニックCD, Sonikku Shī Dī), is a platform video game developed by Sonic Team and published by Sega originally for the Sega/Mega-CD in 1993. It is the first game in the Sonic series to make use of the CD-ROM format, featuring high quality audio and full motion video. Development began in Japan around the same time as Sonic the Hedgehog 2 in the United States. Originally, the games had many similarities, but over time became vastly different projects.

The story of Sonic CD follows Sonic the Hedgehog as he utilizes time travel to save Amy Rose and Little Planet from Doctor Eggman and Metal Sonic. The game features the debut appearances of Amy Rose and Metal Sonic, both of whom have gone on to become recurring characters in the Sonic series. Time travel is a key aspect to both the story and gameplay, with nearly every stage containing four different variations (one for each time period) featuring alternate stage layouts, music, and graphics.