I am that which follows Omega...
Shinryu is a superboss in Dawn of Souls and succeeding editions of the original Final Fantasy. He is arguably the hardest boss in the Dawn of Souls release, along with Omega, but Chronodia takes its place in all versions thereafter. He is encountered on Floor B20, the final floor of the Lifespring Grotto and either he or Omega must be defeated to complete and leave the dungeon.
Shinryu is very adept at wiping out entire parties with ease, as he wields various attacks that all inflict large amounts of damage to all party members. Although Shinryu can use Thunderbolt, Ice Storm, and Tidal Wave, the biggest threat is his ability to cast Flare. With each casting, Flare can either leave the party close to death, KO a few and leave the rest on the verge of defeat, or destroy them outright if the player is ill-prepared. Shinryu's physical attack can inflict heavy damage as well.
The speed at which Shinryu can cleave through a party makes this battle more about all-out power than anything else (instead of the endurance battle Omega ends up being). One should try to be level 70 to avoid being utterly annihilated in a couple of turns (lower-leveled wins are still possible). However, the successive castings of Flare are still very dangerous, even to high-leveled parties. Victory is likely if Shinryu does not wipe the party out in the first few turns, because his 35,000 HP is not well-protected and he is susceptible to high-powered physical onslaughts using the usual strategy of Haste/Temper.
Shinryu is the Japanese name for Shénlóng, literally "god dragon" or "spirit 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.