The Legend of Heroes: Zero no Kiseki Pre-Story: The Ring of Judgment (英雄伝説えいゆうでんせつ 零の軌跡ゼロノキセキプレストーリー -審判しんぱんの指環ゆびわ-) is a manga that serves as a prequel to the game Zero no Kiseki. It was written by Falcom and illustrated by Shinki Kitsutsuki. The manga was published by Dengeki Comics on December 18, 2010 for 850 yen. It was also serialised in Falcom Magazine.
The Ring of Judgment stars the protagonists of Trails in the Sky FC and SC, Estelle and Joshua Bright, who collaborate with Erebonian bracer Toval Randonneur to reveal the secrets of the titular artifact. It takes place in a town in the remote outskirts of the empire, which is retroactively revealed as Alster in the Drama CD for Trails of Cold Steel II.

(Source: Kiseki WIki)