The harvest festival banquet is about to begin. Go to the banquet hall in Hernand Castle.
Rewards: 200 Camp Oats, 1000 Camp Coin, 25.00 Silver, The Grove's Thorn (1H Weapon), Swift I (Abyss Gear) x1, Howling of Chaos (Abyss Gear) x1, Hernand Refinement Token x1

1. Attend the banquet
Head to the courtyard in Hernand Castle. There you will find Barden Middler and Alan Serkis talking to a group of people. Wait for them to finish their conversation, then speak with Alan Serkis.

A cutscene will trigger, and immediately after it ends, the boss fight with Kearush the Slayer will begin. This is a giant gorilla-like monster, so you can forget about blocking or parrying his strikes, you must focus on dodging instead.
Kaerush performs long attack combos, and the only safe windows to deal damage appear only after they conclude. Attempting to attack during his attacks can result in taking massive damage.
The fight consists of three phases, as the boss has three health bars. In subsequent phases, the boss becomes increasingly aggressive and begins using additional attacks.

Phase One
In the first phase of the fight, Kearush uses relatively simple combinations that are easy to predict. The best strategy is to dodge forward-right his attacks to get behind him, land a few quick hits, and then retreat immediately.
Phase Two
In the second phase, the opponent becomes more aggressive and gains new abilities, such as wall jumps ending in a powerful slam or short periods of fury during which he should not be attacked. A grab attack also appears that can deal heavy damage, so you must be ready for a quick side-step dodge.

Phase Three
The third phase is the most demanding, as all of the boss's attacks become faster and harder to predict. At this stage, it's best to adopt a very defensive approach, attacking only after the enemy's full combos and saving your healing supplies specifically for this part of the fight. The key to victory is consistency: repeating the pattern of dodging, landing a short attack, and retreating without taking excessive risks.
Once you deplete all three of the monster's health bars, he will flee from the battlefield, which will end the fight and the entire quest.
A monster brought by the Demenissian delegation to flaunt their military might broke free, instantly turning the banquet hall into a scene of carnage. A fierce battle ensued, and the mortally wounded creature fled, leaving behind a gruesome hellscape of blood and bodies.