Freminet's whole thing is this quiet, internalized intensity, right? He's not throwing grand declarations around. So building tension hinges on translating that into physical details—a glance held a beat too long, the careful way he handles machinery contrasted with a hesitant touch. The silence between you isn't empty; it's charged with everything he's not saying.
I've read fics that get this beautifully wrong by making him suddenly verbose. That kills it. The good ones let the reader's POV do the heavy lifting, interpreting his minimal actions. Maybe he fixes your diving gear with absolute focus, his fingers brushing yours, and then he just... stops, like he's frozen by the contact. The tension comes from the reader wondering what's happening in his head, from the gap between his controlled exterior and the emotions you suspect are there.
The setting feeds into it, too. The underwater scenes, the quiet of his workshop—they create this intimate, isolated pocket where small moments feel huge. A shared breath in the cold Fontaine sea, watching bubbles rise together, feels more intimate than any crowded ballroom scene ever could.