In the wizarding world, head of houses often have obscure and often times perverted privilege. Lords have even more. One of the more obscure privilege is the first plucking. This privilege is only given by daughter-in-law of the houses. Before the ceremony, the first plucking of the bride-to-be is given to the head of house. Often times it is an older male relative. Most often Fathers. Although newer families don't often get to have this privilege as the law though obscure was specific in the required age of the family tree.
Weasley family as a known ancient family just happened to fit this requirement. Arthur Weasley for all intents and purpose is an intelligent man, though often appears foolish. An example is his tweaking of a muggle item, the car, was done so in full knowledge that he has of the law and its loophole. So in regards to wizarding world, Arthur Weasley can, should he want to, walk around the loopholes with blindfold on.
After his decades of marriage with Molly, even a man of Arthur's commitment will face temptation. Even more so when that temptation comes from a world-wide known beautiful group of people. Yes, his eldest managed to attract a veela, one Fleur Delacour.
With a wedding date set, Arthur decided it was time to strike. And two weeks before the wedding Arthur called Bill to his workshop. Mostly as an excuse to be able to call Fleur as well. He gave Bill advice and took his time doing so. A full day was spent on giving him advice. So when Fleur asked Bill what was he doing spending such long time with his father, Bill and Arthur truthfully said it was all about wedding advice.
One week later, also happens to be a week before the wedding. Arthur also planned to asks Fleur to accompany him to the workshop. After searching around the house for a bit he came to find her with Molly in the kitchen.
Approaching them Arthur started with some fake coughs to announce his presence, "Well hello my dear Molly and to you too Fleur dear. Are you beautiful ladies up to anything important today?"
Fleur blushes in sync with Molly. Unused to straight up compliments with no negative intentions. Molly meanwhile embarrassed by the public display of Arthur's affection slapped him whilst replying, "Nonsense. It's just about teaching her our family recipe. What's the matter dear?"
Finding his chance at last to have Fleur, Arthur while restraining his glee decided to tell his purpose, "Well I though about giving some advice to our dear Fleur on advice to handle wedding and Bill. You know I did the same for Bill last week right?" Nods were replied in exchange. "If you're finished I'll be in the workshop alright?" Arthur finishes whilst he leaves.
"Well, you'd better go with him then Fleur." Molly urgently replied
"Are you zure~ mama?" Fleur anxiously replied.
"I'm sure dear, besides Arthur won't give you bad advice. It's best you go now. The recipes can wait."
"Okay then mama, I zhall go." Hurried Fleur as she dusted her hands off.
Walking to the shed where Arthur set up his workshop, Fleur knocks on the closed door. "Papa, it'z me Fleur" She announced.
"Oh come on in, the door's unlocked. Everything is already prepared. Also be sure to close the door on your way in." Replied Arthur with a somewhat strange requests and explanation.
Thinking nothing of it, Fleur opened the door and walked in while closing the door behind her. Subconsciously locking it behind her as well.
Unlike what a workshop entails, the desk are cleared of a lot of items. A new car was under works by Arthur chairs and different wood fixtures are available all around and even a mattress. Arthur meanwhile was facing away from Fleur towards some of the wooden fixture.
"Now that you're here, take a seat where ever you like Fleur dear." Instructed Arthur.
Fleur a bit confused but clear minded unexpectedly chose to sit on a very obscene choice, a wooden horse; which she did not know the use for.
Arthur then turned around and seeing her choice of seat was gleeful and smiled wider. He decided maybe an explanation before what he's about to do may be in order. "Well Fleur dear, you might be confused with what's around you. And what advice I'll give you right?" Here Fleur nodded in reply whilst her footing starts to become unbalanced while she tried to hold onto the horse.
In response to her movement the sliding actually caused Fleur to be excited, unbeknownst to Arthur.
"You see, here in the British Isle, there is a magical law most obscure. You know how nobles sometimes have the rights to a first night. Well as head of an ancient house, so do I." Arthur announced.
Due to her frantic movement on top of the wooden horse, Fleur actually became even more excited which clouded her mind. Juices starts to flow and Fleur started panting whilst holding back a moan. Fleur herself don't understand what Arthur was trying to say. She was only focused on keeping her balance on the wooden horse whilst her body kept moving back and forth from unconscious movement.
Arthur saw what was happening and even the hardening of the nipples of Fleur can be seen through her dress. This incites his hardening manhood. Deciding to cut to the chase Arthur announced and invokes the magical law, "As head of house of Weasley, I Arthur Septimus Weasley invoke the right of the first plucking, so I say, so mote it be" With a wand raised a beam of light suddenly linked him to Fleur.