See anon, the first thing that comes to mind is… anything!

I could see them arguing about most things, sometimes in a more lighthearted way, sometimes not, which is part of their charm as a pairing. They can stand to learn a lot from each other and to see the world through the other’s eyes, see where they’re coming from and either change or agree to disagree. That’s interesting to me. And also it makes for some very funny and cute moments haha.

But since I don’t want to leave you hanging, here is a little list I thought up for you.

—The weather. Yes, really. Dante isn’t used to small talk nor having weather like, in general, so this is bound to be both confusing and hilarious. Might write a whole thing up eventually (it was getting a bit long for this reply).

—Literally how they should walk down a street, apparently (love that home screen interaction to bits). So, extrapolating from that: how they interact physically in normal, everyday situations, even just the uneven pace of their steps when they walk around.
Something like:
“Hey Dante, slow down, I can’t keep up!”
“Tch, my pace isn’t that brisk; you just enjoy being slow.”
“Right, we don’t get to walk around together like that often, so I want to take my time. Is that so wrong?”
"... So you were intent on wasting my time from the start? Hmph, as a reminder, I only agreed to accompany you on this shopping expedition as a favour to the serpent after last night’s meal. But I should have figured you’d do anything to weasel your way out of a busy schedule.”

…and then it turns into a conversation about Eiden’s past as an overworked corporate drone. The ideas just start to flow once you get into it, really. The power of DanEi :3

—Shopping (brands, quality/quantity, how much to spend, etc.)

-A gift idea for a common friend (practical vs. fun/thoughtful)

—Giving advice to others, either what constitutes the best advice or if it’s best to give no advice at all.
There is value in doing things yourself and not relying on others too much. But Dante may not realize how expecting others to be as independent as him would not be realistic for them. It might not seem very mundane but it could pop up very naturally during a conversation.

—Food and cooking, especially if they cooked together. Dante would definitely take it way too seriously but he has no experience and Eiden doesn’t seem very good at cooking either, although he could have improved since the cream stew incident.

—The proper way to stretch or exercise, which could easily lead to sexy times, after a little Eiden-typical teasing.

—(Eventually, and I’m being a little sappy here but please indulge me) Nicknames for each other, a step up from Dante’s good old “kimi to iu yatsu ha”, which is very long lol.
Will we see the great return of Dandy? (Dante: Absolutely not.) Will Dante start calling Eiden by, gasp, his name more often? (Eiden: You’ve been calling me “You” for so long, hearing that now, it’s like my own name has become a nickname somehow…)

And there you go, anon! I hope you enjoyed but if you were thinking about something more specific, do let me know and I’ll reply quicker this time, promise : )