There are some good guides online. I used this one from game FAQs:https://www.gamefaqs.com/ps2/944396-guilty-gear-xx-accent-co...
I do not own, and did not write that guide.
The reason I am writing this here is because the guide I linked is wrong about I-No and there is no way to fix it.
For I-No's path 2 you have to beat Millia after 40 seconds have passed. That will set you on path 2.
Everything else in that guide worked for me when getting this achievement.