I accidentally clicked 'answer privately' when I was writing the answer. So, here is the real thing~!
While KaiMei is an adorably idiot couple, GakuLuka is the romanticaly idiot one.
Luka likes romantic things, yes? Gakupo needs to work extra than Kaito to please his lady.
Who cooks: Well, both are actually good at cooking Japanese food. Gakupo is the best at handling Japanese-grilled-dishes. While Luka is good at making Japanese-home-style-dishes. But Luka always insists Gakupo to trust all the cooking matters to her, tho.
Who does the laundry and other chores: Luka will do mostly the cooking and the laundry. While for the other matters (like cleaning the house or gardening), Gakupo will be tho one who is forced to do them.
How many children do they have: Maybe one. I don't think Luka want too many children, because she thinks they can't really handle too many kids.
Who’s more dominant: Most of the time, Luka.
Favorite nonsexual activity: Have a date. Any place will be fine, examples, theme park, cinema, mall, planetarium, zoo, botanical garden, musuem, etc. They really love to hang out around.
Their favorite place to be together: At night, on the top of ferris wheel, when the the park is almost closed. High possibility they will share a kiss or two there.
Any traditions: I can't think of anything, but I think Gakupo will always try to do romantic things for Luka, since she likes it so much.
Their “song”: Google re kasu? My scumbag brain can't recall any song when it is being asked. wwww.
What they do for each other on holidays: Just do what couples usually do. Date, give gifts, spends time together, and others.
Where did they go for their honeymoon: To a place where they can enjoy beautiful landscape. Maybe with snow, or mountains.
Where did they first meet: Um, I guess when Gakupo, accompanied by Gumi, introduced himself to the Vocaloid family.
Any pets: Maybe Gakupo would like to have gold fish in an aquarium or kois in a pond.
What do they fight over: Luka doesn't like when Gakupo is being wishy-washy or too soft at making decision. Well, actually Gakupo actually just tries to be gentle and thoughtful. But instead so, Luka sees him as a weak guy.
Do they go on vacations, if so where: Maybe onsens, castles (Gakupo's liking), or any region in Japan that has interesting places to visit. Both really loves Japanese's culture and tradition.
