Chaos Oculus

To obtain a Chaos Oculus, you need to find and kill Ruin Sentinels over Level 60+. Upon eliminating these wolf entities, they have a chance to drop Chaos Oculus. Anything above Lvl 60+ also has a chance to drop Chaos Gear and Chaos Axis.

To get Ruin Sentinels to become Lvl 60+, you need your World Level to become World Level 5 or higher. The most efficient WL to farm is WL 6, as enemies are between Level 64 and 84. This will give you the most consistent enemy Lvl past 60+. Anything below, you will find them, but not as often.

To get to WL 6, you need to have completed the following.

Be on World Level 5
Be Adventure Rank 45
Clear Ascension Quest 3

You can get these from the none Humanoid Ruin Sentinels.

Ruin Sentinels are only found on Inzauma, on almost every island. The fastest way to get around is to use the Waypoints, kill, and move on. The image below is where you can find Ruin Sentinels in Inazuma. There are also eight at the tip of Narakami Island.

Comes from a now-inactive ancient Ruin machine. The "Ruin" part of the name comes from the areas where they are most active. However, Ruin machines actually have little in common with the detritus in which they are often found. In the ancient past, these ruins were once part of a civilization mighty enough to almost touch the dome of the firmament, while "ruin" still waits in the deep places of the earth, awaiting the order to arise and tread all kingdoms underfoot.