Ok so this is actually a really easy achievement to get and is technically story related. There are 2 paths in the Extra Story you have to take. Once you enter the Time Nest there will be a rift over to the right by the house (it'll look like the expert missions rifts). Upon investigating this rift it'll start the Extra Story with the mission New Time Rift Troubles. After completing this story this is where the branching paths come from. By the house will be the time rift and after each new mission if you examine this rift it'll take you down one path. However, the other path is when you talk to Fu over on the left hand side of the walkway on the way to the Time Vault.
You'll have to choose one of these paths initially. After you complete the story and the cutscene plays of everyone looking for TokiToki you'll be back in the Time Nest. Talk to Fu again and he will reset history allowing you to play the Extra Story over again but going down the opposite path. So if you talked to Fu for every mission, this time investigate the rifts over by the building to the right. Since you have to do each path, you'll have to play a total of 12 fights.
So in short
1. Start the Extra Story, play the cutscene where your mentor shows up, do the first mission where you fight Fu, Vegeta, and Goku
2. Choose either Fu on the left hand side or the Rift on the right hand side and just keep going through the missions down that one path
3. Once you finish the first path, talk to Fu on the left hand side and he will reset the Extra Story
4. Skip or watch the cutscene where your mentor shows up and then investigate the rift to do the first mission again
5. Go down the opposite path that you chose before, so if you chose Fu first now choose Rift, if you chose Rift first now choose Fu
Upon completing the last mission you will unlock the achievement