Responding to the call of the Azure Dragon Crystal, Lady Celestia transformed herself into an enormous wyvern far more powerful than any mere monster. Shinryu Celestia has sprouted two additional heads that exhale flames and lightning respectively, and she simply swallows those who survive her multi-elemental onslaught. Even the mighty Eidolons are no match for the power of this Secundus l'Cie.
Shinryu Celestia may be nigh impossible to win on the first playthrough, as her attacks hit hard and will probably kill in one hit. She periodically retreats into the darkness, but her eyes glow from a distance allowing the player to predict where she will reappear. Breaksight strikes only inflict 1% of her total HP and she has a flinch resistance of 99 ensuring she will never be interrupted. She receives reduced physical damage—half from ballistic and 0.7 from all others—so magic is the preferred choice. If all of the party die, Bahamut ZERO is summoned. To win the fight, a fully charged Teraflare must hit its mark.
Shinryu Celestia is fought at the end of ELT difficulty in the event "The Battle of Judecca".
Shinryu is the Japanese on'yomi name for Shénlóng, literally "god/divine dragon", an important ancient dragon in Chinese mythology. It is said to preside over storms and rain, and can bring disastrous drought, thunderstorms and general bad weather if it feels neglected and/or angered.
A notable difference between common Chinese dragons and a Shenlong/Shinryu is their fingers; the latter have five on each hand as opposed to four, and they are said to share the same green-blue-ish color as another mythological dragon, the Qinglong/Seiryu (lit. Azure/Blue Dragon).
While the most common Final Fantasy interpretations have four fingers on each hand, other versions also possess five-fingered hands like with the original Shenlong/Shinryu, which mainly apply to the stronger ones.