Online population for the game is long gone, so you will need a boosting partner to level up and then get the trophy.
First you both will need to level up a character to 11 by trading wins. This takes roughly 40 matches. It is important to trade wins one each, because the ranking system seems to be like Tekken endless mode, where you only get experience from oponents near you are rank. The cutoff for Xrd Sign seems to be your level plus or minus 2, and being same level seems to grant optimal exp.
After both are rank 11, one of you will win 14 to 15 straight matches to reach rank 14, and then this person will host the match, and the rank 11 person will have to search for "Rank: Stronger". This is because there's only two settings "about same" and "stronger", hence the rank 14 will never be able to find the match the level 11 is hosting.
Now, after one person got the trophy, me and my partner tried to get the rank 11 to 17, so we could get the other person the trophy, but that didn't work. We played 30 ranked matches straight, ranked 11 winning against ranked 14, and the rank 11 never went up in rank. So what you need to do is start over with different characters, play the 40 traded wins matches needed to get up to 11 and then the 14 or 15 needed to get one to rank 14, and finally get the trophy.
Note: Hopefully along the way you'll get the "Album" trophy for 100 ranked matches, but some people report only getting it after more than 200 matches. I was counting carefully and mine unlock at 101. Some suggest that it might be needed to have 100 on a single character, but that is speculation on my part, could be just glitched or disconnects and/or lag might mess up the counter...