First Battle of the Land of Mountains

The  (第一会戦の山の国, Daiichi Kaisen no Yama no Kuni) was a battle taking place in the middle stages of the Second Shinobi World War. It was part of the conflicts in the Land of Mountains.

Prelude
Following Iwagakure's invasion of the Land of Mountains,, who was still reeling from 's failed invasion, sent Team Shōyō - a team of five Jōnin-level shinobi - to the Land of Mountains to begin countermeasures. After hearing Shōyō had been sent, the Third Tsuchikage,, personally appeared on the battlefield and directed his men towards the location of the Team.

Battle
The battle took place in the mountainous valley closest to the border of the Land of Mountains. Ōnoki, and one hundred of his men, ambushed Team Shōyō in this valley, and a bloody battle ensued. While Ryun, Seireitou, Hikaru, and Echo fought the foot soldiers, Shōyō took on Ōnoki on a nearby cliff side. While it is unknown the exact breakdown of their battle, Shōyō was known to have revealed Sage Mode during the fight, shocking Ōnoki. Try as he might, Ōnoki's Earth Release techniques were failing against Shōyō's kenjutsu and Senjutsu techniques. With no other maneuvers left, Ōnoki unleashed Dust Release: Detachment of the Primitive World Technique, which hit its mark; killing and vaporizing Shōyō on the spot.

From below, it was Seireitou who noticed their old master's death, thanks to his eyes. The immense pain of loss within Ryun and Echo awakened their. At that point, the four grief stricken shinobi renewed their assault on the remaining Iwagakure shinobi. As night fell, the four had cut down over eighty of the original one hundred Iwagakure troops with only minor injuries themselves.

Still enraged by his master's death, and using the cover of darkness to his advantage, Seireitou went on a killing spree among the remaining Iwagakure forces, slaughtering close to forty men single-handedly before his teammates joined the fray to aid him. By early morning the next day, Iwagakure's forces were wiped out and Ōnoki had strategically retreated to regain his strength after his lengthy battle with Shōyō.

Aftermath
The death of Shōyō was stomach churning to Konohagakure, but most importantly, his former students. After this battle, Ryun opted to go to the Dark Forest, the home of the Owl summons, and rest; something which his other teammates agreed to.

This battle awakened both Ryun and Echo's Mangekyō Sharingan, which would play a large role in the battles to come. It was also the battle in which Seireitou earned the title "Shiroyasha" (白い悪魔, White Demon) due to his single-handed, forty man killing spree.