Ah, I see you're a Man of Culture, as well.

Here's another for ya! Lazy Days Moratorium
Truly a sophisticated trope for gentlement only~

That moment when she receives the pizza reminds me of a similar moment in a work by Sugaishi. It's not posted here on FAKKU up to now, but I do recall it was a "WANI"-brand pizza being delivered to the apartment where the girl and her two female friends were having an all-out foursome orgy with one very lucky bastard of a guy.

EDIT: just remembered the title of that work: "Pure Bitch Club", in case anyone wants it for ... er, "research purposes".

Meika is a naughty, uninhibited little minx. She races to the door
half-naked (and stinking of sex) because she wants to tease the
deliveryman (which is a big turn-on for her). Had she been alone,
she might've offered him a "special" tip.

In the classic "pizza porn" scenario, the deliveryman always gets
lucky, of course. The best example is usa's Your Man Will Arrive
in 45 Minutes, which is a 60-page masterpiece---one of the finest
chapters on Fakku.

For another good "lucky deliveryman" chapter,
see Hatimoto's Chimboken's Delivery Boy.

Both chapters are premium high-octane fap fuel.

On page 9, panel 6, Kazu says, "Think of your little brother," but he's not
referring to himself, because he's two years older than Meika (page 20,
panel 1), so I don't think they're siblings.

Also on page 9, panel 6, Meika says, "I'm often naked around the house,"
which means Kazu is visiting Meika at her home. This is further evidence
they're not siblings, and it also means they're (probably) not married. Not
incidentally, it also tells us Meika is a bit of an exhibitionist.

Kazu and Meika clearly have a comfortable sexual relationship, but (as you
note) they don't exactly behave like lovers. Meika is frisky and uninhibited,
with a hearty appetite for food and sex. She takes great delight in teasing
the deliveryman, which (barring any kinks) would be out of character for a
wife or committed lover. I get the distinct impression she might've playfully
offered him a blowjob had she been alone. Perhaps she's promiscuous.

From all that, I conclude Kazu and Meika are fuck buddies, or "friends with
benefits."

Possibly, she enjoys sex with other men once in a while, in the same way that
she'd treat herself to an occasional steak dinner ("If it feels good, who cares?"),
but that's pure speculation on my part.

This is why I love to pore over the details in manga.

I knew a woman who liked to eat hot, spicy pizza during
hot, spicy sex. She also liked to nibble chocolate/peanut
butter fudge whenever she masturbated.

She liked to "stack" her pleasures, so to speak.

Veteran delivery guy to newbie, in a raspy voice: "I've Seen Shit That Cannot Be Unseen." 😱😱😱