I'll be waiting… Trophy in Hatoful Boyfriend

After having completed Sakuya, Yuuya, Ryouta, Nageki and Nanaki's endings, when you start a New Game, you will get a new message: "You can take this chance to fulfill a promise from long ago, or you can live a normal school life this semester. Which do you choose?"

When prompted with the choice, choose "Fulfill the promise" to start the BBL playthrough.

I suggest holding off on this until you've completed ALL of the other playthroughs, so you will get the BBL Epilogue after the end credits of this playthrough. Note that Tohri's ending (#14) is NOT required, as it was newly added to this version of the game, and was not in the original PC release.

While you can make any decisions you like during this playthrough, it IS possible to FAIL prior to the BBL section, causing you to be booted back to the main menu. Thus, I'd suggest simply following one of the routes for one of the regular endings just to be safe. Once you enter the BBL section (it will be obvious), you can make any choices you like and enjoy the story at your leisure.

This playthrough will be very similar to all of your other playthroughs, and you really just need to finish the playthrough however you like in order to earn this trophy. Without spoiling anything, if you have been paying attention and reading the story thus far, definitely read through this one as you play it - it WILL be different from what you expect.

Make sure to save often just in case the game crashes during this playthrough!