Lee Byung Hun is the screenwriter and director of both, and Ahn Jae Yong is the ML in them. Chicken Nugget makes some amusing references to Be Melodramatic including playing the Shampoo Song (one of the 7+ versions) from it. There is wacky comedy in both though Be Melodramatic has much more serious content as well, Chicken Nugget sticking to the goofy comedy.

The direction style is very similar in particular, and the over the top humor, “weirdly wonderful” seemingly the goal, is prominent in both. The stories are both workplace settings, and the characters are extremely… quirky.

Eclectic personalities, exaggerated physical comedy with music frequently incorporated, silly humor by top tier cast members. Wordplay central to much of the humor.
Pegasus Market has a lot of social commentary built into it and tells a deeper story than the silly facade implies. Chicken Nugget does not have any such aspiration. ;)

Heavenly Forest and 20th Century Girl both have strong friendships and a young innocent love story between a guy who in one case opened up to no one and in the other never smiled ... until meeting the female lead. Both involve a lot of photography/filming, and as such, the cinematography of both is beautiful (as are the cast members). A sudden disappearance causes anger and heartache in the one who suddenly is not able to contact the one they love. There are overlaps that do not correlate between the same character (ie both have someone who is ill but the character is not in the same situation).

In both, you'll see heartwarming friendships, a friends-to-lovers situation, a bit of a love triangle (though they play out quite differently and Heavenly Forest's isn't as emotionally volatile, likely because they're in university, not high school), and situations that could make you cry (or not depending on your emotional fortitude/resilience).

The 3 seasons (22 eps) of Seirei no Moribito and Arthdal both have epic-scale worldbuilding from a time long ago with tribes/villages with their own unique lore being important to the story and its main characters as it evolves. Both male leads come from noble/royal lineage of a sort and have 'magical'/superpower-like abilities and both stories have a lot of mysticism in them. The biggest distinction would be the female leads-in Seirei no Moribito, the FL is a 'bodyguard' who has incredible physical capabilities, so the action is intense. Both FLs have tragedy in their backstories though they're very different kinds of tragedies.

Both will sweep you into another world in another era and convincingly craft an entire "world" within the obvious confines that in that time neither place would have, in theory, had much knowledge of anywhere beyond the area right around them even though both have multiple tribes/kingdoms represented in the area that is, nevertheless, vast-seeming despite the Korean peninsula and Japan both being quite small to us now as we understand the universe better.

FWIW, some of the complaints against Arthdal's plot won't likely be present for Moribito... the only pity about Moribito is that I can't find the HD versions (it was shot in 4k resolution, so that being reduced to 540p or 720p is quite a tragedy for something that beautiful with such sweeping landscapes).

In addition to Rain being in both and having pretty contrasting personalities to portray, both shows are bromance-intense supernatural comedies, focus on character growth/redemption, and involve second chances.

Both are part of a trilogy Jupiter Films produced about folklore in the Joseon era ie your fortune linked to your family grave locations, facial structure determining if someone is fit to be king or queen or will bring disaster etc.

Both are part of a trilogy Jupiter Films produced about folklore in the Joseon era ie your fortune linked to your family grave locations, facial structure determining if someone is fit to be king or queen or will bring disaster etc.