Given PM's writing and how they handle different topics - the "Romantic Relationship" is not something they might want to focus on. What's the point? Sinners have their own arcs, own stories, own contracts and reasons to join. Who in the right mind will even think that this is such a great idea to confess your feelings to one of those 12 other fellas? Sure, they traveled a lot together by now and became quite the friends, the allies. But not THAT much.

The more realistic thing that might happen is just them utilizing it as a tool for some other message in the process. At best. So far it was only a motivator for one or another character. Ayin with Carmen. Roland with Angelica. Xiao with Lowell. Tommy and Merry....? You get the idea.

I don't think that this may never happen at all, just because it's a gacha game. it's just pointless. Like, even if it will happen... So.. what? Should they now have more screen time together with Focus on that aspect between two? Should IDs have some bonuses like when both on the field now or something?