An Error in Calculation is the 9th side mission in Nioh 2. This walkthrough will guide you through all areas of the An Error in Calculation Side Quest.
An Error in Calculation is unlocked when you complete The Hidden Monster of Okehazama Main Mission.
Recommended Level: 27
Requirement: Finish The Hidden Monster of Okehazama Main Mission
Reward: Warrior’s Cross Spear, Abacus, High-Quality Leather Platelet x3, High-Quality Leather-Cord x3
Once again your only objective is to recover a single item from a specific place in the map. Follow the path through the tunnel and once you reach the cave with the Jelly Yokai, take the left path (the only available) to reach the outside section.
Once outside cross the tree-bridge and you will have the choise to either follow the path or entering the Yokai Realm in the cave. The cave is where you have to go.
Inside you will be greeted by an One-Eyed Oni, an Enki and a smaller enemy playing a biwa. Try to lure out the big guy first, since you don’t want to fight them all at the same time. Once the cyclops is done, you can sneak hugging the left wall to the guitarist to dispose of him. Take care of the monkey next and prepare for the ugly big guy in the next room.
The big ugly Yokai called Waira is the one you have to kill to get rid of the Yokai Realm. Take him back to the room where the monkey was and take advantage of the rock pile in the middle for an easier fight.
Once the enemy is down, the Realm will disappear and you can head into the room the big guy was in. Loot the chest there and the mission will succeed.
This finishes An Error in Calculation side mission in Nioh 2.
For all other Mission Walkthroughs, check out our complete Nioh 2 Walkthrough.