I hope you both intended this as looking at them as a ship because that's what my brain is full of that's what you're gonna get
Pillow fights. Paint fights. Snowball fights. Water fights. Food fights that always start with a little playful flick of sauce here or there and "Now, look, we must be mature about this and not make a mess" and always end with them both laughing and covered in mashed potato
They sometimes stay up way into the night just talking, about heroic things, about memories, and war stories and battle songs and old friends and musings on where they might have gone wrong, but also about really random junk that happens to be on their minds and they discuss it no less deeply because they're that comfortable with each other
They go for runs together. They race each other now and then, naturally. Last one around that bend has to make breakfast!
They also do other exercise together, like dual sit-ups, you know, when your legs are interlocked to balance each other out. And once Saber pulled into a sit-up and Dia was already there and she bumped right into him and he smooched her on the mouth and she fell backwards and blushed for like five days
It's not all hard work, though, they love just lounging around watching TV together... and complaining about in shock and awe/making fun of things like late night infomercials
Also VIDEO GAME WARS
Dia takes every opportunity to dote on Saber (even though they take it in turns paying for dates) especially with food. He likes to treat her and see her happy
And she can eat AND drink him under the table any day and he's really quite impressed by it
They have lots of increasingly stupid in-jokes
"When we get home, I'm going to tear all your clothes off." "Not if I tear yours off first."
