I rly tried to look past the age gap thing but they keep mentioning every chance they get ...

Grooming means to train a person to their personal taste lol. Age difference has got nothing to do with it

If anything, Kotaro groomed Mizuki lmao. I remember earlier he thought of Kotaro as a cute little brother type until he became a man.

This is the definition I got from my country's police net website: Grooming is when a person builds a relationship with a child, young person or an who's at risk....(this is literally what happens in the story. The age difference wouldn't be so bad if it wasn't for the grooming )

.....what?? pls tell me your joking. let's be serious for a second, whoever told that's the definition of grooming was lying to you or you read that off of a porn story or something.
@Ottarantology is right about the grooming in their relationship, sorry to say.

Yes to build a relationship with a child but that's not what happened here, mizuki just thought of him like a little brother till kotaro became and adult. So how is that grooming?

Thats exactly what grooming is. You trap a kid and groom them to your personal tastes, as you bind them in relationship.
Exactly why it's calling grooming

So what your say is he built a relationship with a child and started dating that child when he came of age...so grooming?

Thank you, I'm here for the smut but fuckin hell why the fuck it's written like this

Did mizuki and kotaro has a romantic relationship when kotaro was young? No. Did mizuki do anything inappropriate. No
Explain to me, what part was grooming

Grooming isn't dating a child...that would be pedophilia. Grooming is when a person builds a relationship with a child, young person who's at risk and that's exactly what happened Mizuki built a relationship with a four year old child and continued said relationship.When that child came of age he started a romantic relationship with him.Their age difference is 12 years actually and I could get past if the seme didn't make weird comments like "i've raised him well" and the "badump" when he was proposed to by a child just adds to it.

He clearly said he saw him as a brother till the time Kotaro came of age. Haven't you ever been confessed to by little kids or seen some kid do it. Anyone would find it cute, its just cute. Nothing else. That's what mizuki felt when kotaro was a kid. If it was grooming Mizuki would have always thought that he'll date kotaro when he grows up even when he was a kid. But it's not like that

But it is like that tho, he dated a child whom he practically raised Mizuki watched him grow up and started dating him immediately when he became an adult...that's grooming 101