Both have female leads who are wanting and hoping for recognition and love from their own families and are mistreated badly. Both have a influential/rich male lead that will do anything to protect and help the female lead. Both have a revenge/thriller aspect, but not in a similar sense. Chemistry between leads is great in both!

Both series have a seemingly cold/uncaring male lead that gets into dangerous situations and hides secrets but in actuality cares deeply for the female lead. Both series have a mystery element and both series have great visuals. The chemistry/tention between the lead characters is uncharted and it keeps the viewers in a chokehold.

Both have a strong and smart female lead that disguises themselves as a man. There's also a scheme to overthrow the rulers and kill the crown princes in both of the dramas.

Alchemy of souls season 2 contains romance and magic just like Lovers of the red sky. There are similar special effects. In both series there are also otherworldly powers standing between the main characters.