In order to obtain this achievement, you must infuence Nona so she and Ren don't end together. There are three key moments in which you can do it.
- At the beach, when playing "Truth or Slap", when Clarissa asks Ren if he likes Nona and he denies it, say that he's lying and that he told you before that he liked her. When the boys go towards the cave, follow them and don't talk to the girls.
- At Adler's Estate, when searching the house, don't talk to Nona, or, if you do it, don't talk about Ren.
- Finally, when you are on Bridge Stand in order to send the signal that opens the bomb shelter, you'll enter on another of those time loops. Before using the tape recorders in the bridge, don't talk to Nona, or, if you do, tell her
"It doesn't matter".
Also, you can combine this with your "The strong, silent type" playthrough, as the fact of don't talking all will result on Ren and Nona not dating.
If you meet these requirements, you'll obtain the achievement during the "stat count" before the credits.
For a guide on how to get all the ending achievements in the lowest number of playthroughs, click here