Enter the Cult of the Curse Mark's base at Mount Pisga and take down the members. (And get Clippy his S-rank promotion.)
After a run in with some bandits in the forests of Oto, Eclipse uncovered evidence of some sort of cult centered around the curse mark developed by Orochimaru. The bandits led him to one base, where he encountered more members, but also evidence of a leader and another location important to the cult.
Eclipse met with Amaya, Jeisen, and Zenko a distance from their location. After some discussion they headed out. It took them some time before they found a brook that gave off a sinister aura. They followed this to a pool with a waterfall and cave. After some puzzling they released seals that drained the pool and revealed a hatch. Eclipse was able to unlock and open it so they descended into the base. They ended up in some dingy supply room first and had to maneuver through to a set of double doors, which Amaya broke down. This drew out the inhabitants and a battle started. It was a difficult fight between the four ninja and their four opponents, but they managed to destroy all those present. (And Clippy was promoted to S-rank.)