Sid Eternal is a free-to-play Android game developed by Leaf Contents Alliance Corp. It is a card game that offers over 1,000 unique Sidians for players to collect. The game is based on defeating the enemy 'Irregular' during class and exploration to obtain cards called 'Sidian(s)'. These cards can be fused to upgrade their level and skill. There are five rarities of Sidian, ranging from 1(normal) to 5(S.Rare).

The game offers a variety of content for players to explore, including Magic Dungeon and Production Dungeon, where players can obtain Sidians and production materials. Players can also manage their own Sidians in the Dorm, level up their skills and fuse them to create stronger units. The Exploration mode allows players to obtain various items, materials, and experience a unique story. The Atelier feature allows players to craft items using materials obtained from the Production Dungeon and Exploration. The Library provides players with details on Sidians, unique story, and mission. Additionally, players can create or join a Circle to get more rewards and conquer raid with other Circle members. The Heroes Forest feature allows players to summon special Sidians by confessing their love to them using a love letter. Lastly, the Shop is where players can purchase items or summon Sidians.