Black heart event:
>Exit your farm towards north.
You will see Gray. He will then notice you and goes in the Blacksmith's shop. Then he will say, "So cute...". Saibara then will say he came here to be serious in his training and Gray said no. Then he will be chased out of the shop, then he will notice that you saw that then he will walk away.
Purple Heart Event:
Blue Heart Event:
> Seen the Black heart event
> Inside the mine behind the waterfall
> Sunny Day
You will see Gray. Talk to him and he will say he is looking for a silver ore. Give him one and he will be happy towards you.
Green Heart Event:
> Seen the Blue Heart Event
> Outside of your house
You will see Gray waiting for you to come out and he will ask you if you like wearing jewelry. Answer "yes" and he will give you a necklace.
Yellow Heart Event:
> Seen The Green Heart Event
> Rainy Day
> Exit your farm towards north
You will see Gray and his grandfather, Saibara, arguing about his training. Then, you will go near to him and he will leave immediately.
Orange Heart Event:
> Seen the Yellow Heart Event
> Have your house extended twice
You just woke up, You will see Gray in your house and he will say he can't train in a place like that. He will then state he wants to use your watermill until then.
Next day, when you go out from your house, Gray will say he had weeded your fields.
Next Day, when woke up, Gray will call out to you. Then, he will ask you to test out the hammer that he made. Once you test that, the hammer will break into pieces. Then, he will leave your farm disappointed.
Next day, go out of your house and Gray will talk to you. He will say that he had underestimated being a blacksmith. He will go back training under the old man.
(Note: When he's using your watermill in three days, you won't see him anywhere. Farm, in the village nor mountain, you can't see him)
Red Heart Event:
> Seen the Orange Heart Event
> Go to the Blacksmith's Shop
You will see Saibara praising Gray for once. Then Gray will thank him and he will see you. Saibara will go to the other room and leave you two in your own privacy. Gray will confess to you and ask you to marry him. Answer "yes" and you two will be married in a week.
To get Gray to a higher heart level. Give him ores, eggs, wine etc. Everyday. You know the stars below your character's name, those are beauty icons. Just talking to him will rise his heart level.