This is fun, this kind of started out as a joke and then now it's one of my favorite songs it was one of the first ones I wrote for the album when I was getting out a lot of energy and hadn’t written or been in a studio for a long time and then this came out and I really like it now."
-Harry Styles

Though Kiwi has a controversial and explicit lyric about the obsession someone has with an eye-catching woman, the music video sounds totally irrelevant to the lyrics since it's filled with children, sweets & puppies
But why should the music video look like that?
I don't think he spends his time to make a meaningless music video
-this is my own interpretation-
-E.M

Well at the first scene we see a girl dressed up like Harry which may be the symbol of someone he cares about, they are related somehow, and she's holding a box of cupcakes in her hand
The song goes like this:
“she worked her way through a cheap pack of cigarettes”
Then the camera zooms on cupcakes
Sweets such as cupcakes that are shown in the video actually carry out an important message throughout the whole video, before starting the interpretation lets jump to this part of the lyrics which says:
"she sits beside me like a silhouette
Hard candy dripping on me till my feet are wet"
As you noticed, he is comparing the woman to a hard candy which is taking all of him, a simile which also appears in the video. generally speaking, sweets in the video are the symbol of women like that. (you know what i mean.)
"hard liquor mixed with a bit of intellect"
The other children in the sports hall are a sample of our society, they are standing, with a sense of greed, some of them have sweets in their hands and others are staring at the deceptive ones on the ground, which might look good and delicious but are not healthy. being on the ground worsen the situation, they are free and good-looking even though they're not as eatable since they're on the ground, but children don't care, right? they are lustful and they look angry as they are going to fight
"and all the boys there were saying they were into it"
Children are into the sweets, unconscious of how detrimental it is
Just like adults when they can't control their temptations
"she's driving me crazy but I'm into it, but I'm into it, I'm kinda into it"
Video emphasis on the sweets that are on the ground, they look extremely adorable, nice, tasty meanwhile they are inwardly bad & harmful
The girl who's walking down the hallway uncovers the box of her cupcakes while she walks towards the sports hall, she's a symbol of an innocence person entering the society, she has her own cupcakes which are unhealthy as well, but at least are not lying on the ground and therefore are not dirty. they might even be homemade. ( since we're all human we all have the potential to make mistakes and do sins, but entering the society reinforces it.)
The song goes on like this
"i think I'm losing it..."
Children in the sports hall are starting to lose their control, they are angry and their eyes are filled up with lust and greed, they are willing to start a fight
"I'm having your baby
It's none of your business"
The girl is still walking down the hallway, in the sports hall, some kids have started to taste sweets, some of them are busy pointing out each other, seems like they'are blaming each other over the sweets, they're greedy, mad and angry
The lyrics are pointing at unhealthy, toxic relationships which are just based on sexual wantings and no love, ( having someone's baby has a reference to sex.)
"it New York, baby always jacked up"
The girl finally enters the sports hall, New York stands as a sample of the society, the girl puts her box down and grabs some cupcakes from it. while she's looking around to see if she's could start a fight, a boy with a fake cigarette stares at her and gives her a smirk with a message like "you don't dare to do that!" (cigarette represents the class of the character)
That's how we get involved in the society, we are innocent but we're willing to prove ourselves to the others (especially the ones in the upper class.) and that's how we get affected
So she starts the fight, some are scared, some are angry, some are greedy. they all immerse themselves in the fight. everywhere gets dirty, their clothes become covered by sweets. they're not neat anymore....
As the video goes on, suddenly the girl finds out her box has become empty so she goes for more! she grabs sweets from the center of the hall, she poorly crawls on the ground, with that sense of greed, just like others or maybe even worse
"she sits beside me like a silhouette
Hard candy dripping on me till my feet are wet
And now she's all over me its like I've paid for it
Its like I've paid for it
I'm gonna pay for this!"
She's crawling, on four feet, the way animals do, basically, it mentions the way greed and lust nullify human actions. when you do something based on lust it becomes worthless and usually brings bad consequences
In the video, the children couldn't control their lust over the sweets, and the girl, who wasn't even that much into the sweets got involved to just to prove herself to the others
Their behaviors have bad outcomes, they became nasty and some of them got sick (as we see at the end of the video) they didn't pay for the sweets, but they'll have to pay for its results
The lyrics of the song and the video totally match! having a sexual relationship just because of lust, without any background has bad consequences! not just the possibility of baby-making as the song mentions but the feeling of regret, mental sickness, loss of innocence &...

As the girl continues to crawl with her clothes covered by sweets, Harry, carrying a puppy, suddenly opens the door and sees the girl in that situation. the girl wasn't ready to see him. she stares at him with a special feeling as if he cares about her and her innocence
Harry gets mad, seeing her in that situation, he releases the dogs inside the hall like he doesn't care anymore. he has lost his mind. the dogs get inside the hall, as the chorus plays again, we can feel the violence for another time. the dogs, which are a sample of animals, get mingled among the children. now their actions are the same, they fight, they eat and they don't think
Some are still greedy, some still fight, some are frightened and some got sick. it indicates people's different reactions to the society. some people never quit doing bad things, some regret after doing those and some just try to survive
As we see at last moments of the video, Harry gets into the hall and hides behind some chairs with a girl beside him, they're scared. Harry looks around and unconsciously grabs a cupcake, even though he knows it's not a good thing to do, he gives it to the girl beside him to throw
Sometimes as a reaction to the unwanted things, we make sudden decisions which make us regret after. that's what happens in the real life
Than camera goes on two kids, one of them is sick and the other is crying out loud (bad consequences) which make Harry overwhelmed & upset
In the last scene, they're taking a photograph, they stand next to each other like everything is fine while the traces from sweets are still there, on their clothes and faces. some are more affected and some are less. but among those children, Harry is still clean even though he went to the sports hall, that's why he smiles
The last scene has an ironic message. it means we're living in a sick society, where everybody has problems, they do bad things, they get affected by each other but after all, you can be among them and don't accept negative effects. you can stay the same. you can remain nice
-E.M

Here is also a beautiful poem from Rumi, which somehow indicates the same meaning:
The world is a play, a children's game, and you're the children
God speaks the truth
If you haven't left the child's play
How can you be an adult?
Without purity of spirit
If you're still in the middle of lust and greed
And other wantings, you're like children
Playing at sexual intercourse
The same with the fightings of mankind it's a squabble with play-swords
No purpose, totally futile
-RUMI (selected poems)