In the Lost Lands, this is the resting place of all the spirits of past Kages. It doesn't matter what village they are affiliated with, they all come to this Island. It is said that Shadow Island is shaped like the Shadow Village's symbol.
When Rai first walked in the Lost Lands, he saw a figure in a white cloak. He followed the figure to an island covered in forests, and a gigantic cavern in the middle of the island. Rai walked through the area, and came across a tablet which read:
A legendary power is given in this cave. The legendary power is a blessing for the clan who can supress the power of the Kyubi only.
Rai was perplexed at this inscription, and read further:
If there was to be one who took the legendary power, or if the person wielding the legendary power, and was not of the clan who can supress the power of the Kyubi, that person shall immediatly die. If the thief, or person is not of the clan who can supress the power of the Kyubi, is an immortal, they shall be stripped of their power, and cursed to walk the earth for 1000 years. They shall also be given a cursemark, so that no matter who they meet, all shall shun them, until the cursed person repents of their sin to The One Who Is Holy. Only then may they be returned to their previous status.
He realized that the clan was the Uchiha. He was amazed that the land he was on was a shrine to the Uchiha of old. He then read on how to obtain the legendary power:
Those who seek power, show the power of the clan who can supress the power of the Kyubi.
The first test is a test of lucK, you must face three paths. Choose wisely, the right pAth will lead to the next area. Choose unwisely, and ye shall be dead.
The second test is a test of power. You must find a way to defeat the GuardIan in this room. Never underestimate theiR power.
The thIrd test is a test of wisdom. You are faced with a room of cups, each made with gold. You must fiNd the one thAt Is the one that The One Who is Holy's Son made.
The final test is a test of couraGe. You will be faced with wArriors that are heavily armed. Find the weakNess for each, for they all have a weakness.
Rai read each of the instructions, and he found that the legendary power was an ocular jutsu. He read each in line that some letters were capitalized, and bolded. He read the word: Kagirinaigan, the unlimited eye, he translated. This is how one is to obtain a Kagirinaigan.