1. Upload your save to the cloud on PS4 by going to Options>Cloud Options>Upload Cloud Save from the Main Menu of the game.
2. Start the game on your Vita. When you get to the main screen choose to start the game using the cloud save instead if local when it asks.
3. On your PS4 go to Online Options and turn on the Cross-Play option. If you don't you won't be able to connect to your Vita.
4. Go to League battle on both systems and make sure it says you are on the same percentage toward the next rank (this method is apparently easier if you are Saturn rank or above due to less players in the rank).
5. Search for a game at the same time on both systems. Do it about a second earlier on Vita due to the slower speed that it launches the search.
6. If you are paired with yourself both systems should show the [Connecting] dialog and then they should both disappear at the same time. You'll see that it shows you are paired up with yourself.
7. Start the game and win on your PS4. Once you are taken back to the League Match menu quit the game on Vita, then go upload your save again on PS4, then repeat from step 2.
Si alguien me quiere agregar, tengo PS4 para sacarnos online el trofeo de 5 victorias seguidas, mi psn id es: isanchezgl