This isn't entirely avoidable, but will depend on which Reyvateil you are romancing. If you are choosing Finnel, you will not obtain this trophy, so be warned.
After the events of the Garvelt Bridge and the Lymph Vessel, you will return to Archia and be prompted to rest at the Eulark Inn to progress the story. This is when this trophy and scene will appear, only if you have given a Heart Point to Saki.