Same cute, simple and uncomplicated storyline. There's not much going on, the story is not complicated, but it's refreshing at the same time.
They're both set in school, and deal with some family issues that don't usually get brought up much in BLs. Blueming is a bit more serious about it in how they deal with theirs but both are surprisingly realistic in how they approach the issues.
As a result, both series have a lot of heart in them through the sense of honesty in how both are written and how the plot progresses. Blueming is a little more bittersweet and serious than 21 days but still ends happily, plus they have more kisses and sweet moments between the couple.
Both shows also have a one sided enemies/rivals to lovers main pair with a prickly tsundere.
As a result, both series have a lot of heart in them through the sense of honesty in how both are written and how the plot progresses. Blueming is a little more bittersweet and serious than 21 days but still ends happily, plus they have more kisses and sweet moments between the couple.
Both shows also have a one sided enemies/rivals to lovers main pair with a prickly tsundere.