When I was reading Kasa no Shita, the image of bitter-sweet, triangle love between Hitomi, Ryuu and Hikaru from Hydra/Rules pooped up in my head right away. Both mangas give similar feeling of mixed emotions, strongly affecting its readers, making us love and hate certain characters and feel strong connection with them. The storytelling is also quite similar, drama and amazing art mixed up together. One of characters notice feelings the other two have for each other in both mangas and he's tring to go between them, snatching one for himself.
Both mangas are going to break your heart in some moments, so better brace yourself.