
"You need to kiss me to greet me" and "you have to hold someone's hand while in the palace" now, because everyone is attractive this does not raise a red flag to you.
Now picture this, there's an 18 year old boy and a 12 year old girl. He says to her, "where's my kiss?" And "you have to hold my hand" what are your thoughts now? Grooming isn't just forcing yourself on someone, it's slowly getting them comfortable with the idea of casual intimacy that then leads into a relationship.

They have been only doing peck on the cheeks and holding hands only. The thing you are asking me to imagine is gross when it comes from an already adult person and a 12 year old. And the explanation you gave about grooming, then all of us have been groomed or grooming another person. When people have romantic interest they start to make another person comfortable with their presence subconsciously. Otherwise it won't lead to anything. And no you just don't randomly start having feelings for someone.
Here they were childhood friends and started holding hands and a peck on the cheeks as greetings when they were both kids. Even we did that with our friends as kids as well.
I'm pretty sure they stopped sleeping together when the emperor was an adult and aware of his own feeling towards Bun.
Again you can not apply the 21st century context to this story's timeline. The ML's actions are simply from overly obsessive personality of his (which is not justifiable). But you are also overlooking the MC's feelings towards emperor since childhood and labeling his feeling as being groomed.

Yes, the 12 year old would only be pecking the 18 year old on the cheek. Nothing wrong with that, right? And obviously my explanation is not about people of the same or similar age/both of legal age. Don't be stupid on purpose.
The king was 21 when he became aware of his feelings and did not cease the physical contact, otherwise Asha would have stopped doing it buy now due to the king setting a boundary with a minor and then that minor growing into an adult that has already stopped doing stuff like that.
Of course if that 18 year old is making that 12 year old feel special then they will also develop feelings and a dependency. Especially when there is a major power imbalance like this. The excuse of "21st century context" makes no sense, seeing as everything happening is utter fiction. Like really, which country historically has secret tablets that allow you to marry a man?

Exactly, people just want to be dirty minded for no reason. Probably they never read the story and just read the beginning and came to the grooming conclussion. But it becomes quite clear that their relationship during childhood was innocent and that ML never disrespected him. Imo it was impossible for ML to have the mind of a groomer back then, he was just childish and inmature in the past. And even when ML became an adult he was still inmature, to the point he even sent Asha far away from him for 4 years just because he accidentally ignored him. Also in their interactions together through all the manhwa there is never an unequal dynamic, they treat eo with respect and enjoy eo's presence. Overall this is giving more a childhood friends to lovers trope than anything else
The way people calling everything grooming these days seems persuing the person you love grooming as well. Yeah, it seems bizzare cause we are exposed to the emperor's inner most obsessive thoughts. While we don't know anything about the steam bun.
But going forward we see our steam bun has feelings but he couldn't act upon it or most likely brushed it off because his family and law doesn't allow that. Also, not to mention while the emperor was busy making his own move (which is morally wrong but he was getting older as well) our steam bun sorted his feelings himself without manipulation. Also he didn't once sexually harassed or pushed himself on the Bun.
Also it is my own observation but the Emperor knows as well that Bun is too dense to figure his feeling out that's why he was making arrangements in his own way.
Another point, it's freaking ancient era no body gives rats ass about feelings or consent. Marriage is done for political advantage here. Not to mention he's a freaking emperor he could have done worse changing the law himself or locking him up with honey traps.