Thank you! I'm so glad you enjoyed it. Off the top of my head I believe you get that CG by romancing Bemelle, saving Lu, and then on the island spending time alone with just Bemelle (so you get the CG where he's holding his sword). Keep playing through and you should get it before the start of the second night.
If that's not it let me know. I wasn't able to check the game itself because I have to leave the house right now, aha, Good luck!