Homegirl

My friend has been budging me about this, So I'm back at it again...(hoping someone recognises this manhua/manhwa)

1. It's bl.

2. "kinda" isekai (Like the mc is transmigrated to his sister's (?) book.)

3.The Mc is the older one, with purple long hair.

4.The Ml is the younger one with green long hair. And Manipulative (?)

5. So, there was a scene where the Ml drowns a cat...just cuz it was getting more attention from the Mc

6. In the real world, the Mc used to draw smut (bl?)

7. According to my friend, the Mc was a bit...stupid? And easily manipulated?

8. Ml is kinda a psycho?

9. They met as children and grew up together.

10. The ml wasn't supposed to be the crown prince but after some royal drama...He was like slowly rising from his position like as a lowly, yet important prince.

So, it's my friend's b-day tomorrow, and she wanted me to find a manhwa/manhua she was reading (Yes. She forgot the name)
The details she remembers :
1. It's bl.
2. "kinda" isekai (Like the mc is transmigrated to his sister's (?) book.)
3.The Mc is the older one, with purple long hair.
4.The Ml is the younger one with green long hair. And Manipulative (?)
5. So, there was a scene where the Ml drowns a cat...just cuz it was getting more attention from the Mc
6. In the real world, the Mc used to draw smut (bl?)
7. According to my friend, the Mc was a bit...stupid? And easily manipulated?
8. Ml is kinda a psycho?
9. They met as children and grew up together.
10. The ml wasn't supposed to be the crown prince but after some royal drama...He was like slowly rising from his position like as a lowly, yet important prince.

That's all she remembers...Any clues or help is appreciated!
Thank you!