Friendship between the girls is the concept of both drama and movie. And also the envy that is growing when one of them become succesful.
Both dramas present the struggles of high-schoolers in order to become no.1. And also, both dramas have kids forced by their own parents to follow a certain path in live they actually don't want to.
Both movie have same kind of concept. A boy is forced to became a monster. If Hwayi: A Monster Boy presents the story of a 'not-wanna-be-a-monster' boy, in Monster, the lead became a monster by his own choice.
Both leads have a supernatural power and that's why they're using their power to save others. You can see a good-evil 'fight' in both dramas.
These 2 dramas are kind of similar. The male lead is an idol who's totally a jerk while the female lead has a strong and crazy personality. The first love of the male lead is also a famous singer and you can see scandals in both dramas. They're combining music with love and another similarity is that the leads are fighting with each other in the beginning.
Both dramas are about music industry. In both you'll be able to see a group of 'kids' trying their best to debut, true friendships and loyality, love between an idol and a non-idol, achieving dreams, dating issues and the most important: a music company lying fans in order to cover their idols and keep their company up.
In both dramas the female lead is a celebrity who has her own career standing on the edge, while the male lead is an alien who has to live a limited time on the Earth and they both fall in love.