Junior college student Dylan encounters the winged android Stella, who falls from the cloud realm The Vault, and the two form a lifelong Contract Bond. Dylan integrates Stella into daily campus life, drawing the pursuit of Lord Milo, the keykeeper of The Vault, who has come to retrieve Stella. The arrival of Type B Recon Unit Nora reveals more secrets of The Vault. Dylan stands with his friends to protect Stella, fighting against the orders and constraints from The Vault.
