Find Gekomatsu the frog at the foot of the stairs heading to the Hokage's Mansion. He will give you a quest to find chakra fragments. This is a multi part quest. Each fragment you pick up is worth 20 points and fragments respawn after leaving the area and going to an area beyond the one next to it. At 500 he updates your quest and gives you chakra entities. After that he gives you 2 chakra entities for every 1,000 chakra points; except for 10,000 he gives you 1 entity (and a timeline page).
Stage 1: 500 chakra fragment points
Stage 2: 5,000 chakra fragment points *
Stage 3: 9,999 chakra fragment points
Stage 4: 10,000 chakra fragment points **
*Once you have the 5000, Gekomatsu will ask you to go to far west of land of lightning. What he means is go to the land of the last battle. There will a purple chakra fragment with a dark aura in the center of the area. Interact with it and you start the Eternal Mengekyo Fragment; where you play as Sasuke trying to get away from Tobi and Zetsu.
In the first part just sprint passed all the enemies to the other end. Saves time and health. The second part is a mob battle with a bunch of Zetsu clones. The third part is a battle with Tobi (Zetsu clone); during this fight make sure to do the bonus requirement so you can get the Big brother, Little brother timeline page for the Historian achievement. Once you have beaten Tobi and have watched the cutscene the achievement will pop.
**In order to get another timeline page you must continue on with Gekomatsu's quest. After doing the special fragment he will update you quest to having to get 9,999 chakra fragment points. Do that and then return to him. He will give you more chakra entities and will update your quest one last time. Now you have to get just one more fragment and then go back to him. Once you return to him he will give the Three Years timeline page.