If Kazuma Kiryu Were Your Boyfriend
If Kazuma Kiryu were your boyfriend, he would take you out to eat at the restaurant of your choice, no matter what it was. Well, provided it was ramen, or beef bowl, or somewhere with a bar. He wouldn't let you split the bill, either, but mainly because math isn't his strong suit.
If Kazuma Kiryu were your boyfriend, for the first few months of your courtship he would never fail to bring you flowers, even when you tell him -- repeatedly and emphatically -- that the gesture is wasted. You will make a show of tossing them aside and chide him not to do it again. Ever the gentleman, he will pretend he doesn't know you always bully an underling into getting a vase and watering them after he leaves.
If Kazuma Kiryu were your boyfriend, he would vanish abruptly on the day of your birthday and roll in about 10 minutes to midnight covered in bruises and carrying the perfect gift. Asked how he was able to track something like this down, he will stare straight ahead and exhale steadily, then tell you not to ask questions about his past.
If Kazuma Kiryu were your boyfriend, it will not even upset you the night he comes home and explains, slightly bewildered, that he somehow got roped into being an exotic dancer. It doesn't even rank in the top 10 strangest things he's done this week.
If Kazuma Kiryu were your boyfriend, you would soon lose count of the seemingly endless supply of tiny adorable orphans who seem to gather around his feet. You will never, ever get all their names right, and can't imagine how Kiryu-chan manages it. They regard you with suspicion and at least one of the girls seems ready to shiv you if you ever take her Uncle Kiryu away from her, but she warms up significantly after you let her paint your nails the most garish hot pink ever devised.
If Kazuma Kiryu were your boyfriend, after the child has completed her handiwork he will tell you the pink looks good on you. The worst part is that he will be so earnest when he says this that you're forced to go lie down for a while.
If Kazuma Kiryu were your boyfriend, you could spar any time, any place. And you would. Your bodies would become living canvases of purpling, mottled bruises and long, spidery cuts from a few well-placed knives, and all of your subordinates would wonder what the hell the two of you have been up to. Your mutual acquaintances, who know you at least a little better than that, don't have to ask.
If Kazuma Kiryu were your boyfriend, you would go through three headboards in a single year and more sets of handcuffs than even you want to think about.
If Kazuma Kiryu were your boyfriend, everyone would know it, because you aren't exactly the discreet type.
If Kazuma Kiryu were your boyfriend, you would periodically butt heads on whether to spend the night in (Kiryu-chan's preference) or go carousing around the red light district doing violence to your livers. This at times escalates into arguments over slightly less trivial things, and from there into a knock-down slugfest on the kitchen linoleum. It's awesome and the sex afterwards is great.
If Kazuma Kiryu were your boyfriend, you would finally figure out what all these fucking iron gears are for.
If Kazuma Kiryu were your boyfriend, one morning you would wake up from a chlorofoam-induced blackout to find yourself tied up and locked inside the trunk of an unknown car, and you would sigh because these kidnappings are becoming routine for you now, and you aren't sure how you're supposed to feel about that.
If Kazuma Kiryu were your boyfriend, after you had twisted out of your restraints and kicked your way to freedom, you would ask youself if this is really the life you want; if any boyfriend is really worth all this trouble. Tearing a path of devastation through the enemy compound with only a baseball bat and a knife, you would resolve that, in fact, it isn't worth it, and the next time you see Kiryu-chan you're going to tell him it's over.
If Kazuma Kiryu were your boyfriend, when the two of you finally reunite in the shot-out remains of a warehouse, you will rush into each other's arms and all these thoughts will vanish from your mind. You will punch Kiryu-chan in the mouth, aggressively, with your mouth. It will be good and the adrenaline rush from being grazed by three bullets will make it even better.
If Kazuma Kiryu were your boyfriend, all of the above would pretty much be canon. Certainly the writers are in on it.