Two points of similarity we find in both of the series; food in some form (chocolate in Shitsuren Chocolatier and Italian in Bambino!) and the ML is Matsumoto Jun too.

Both the series deal with "monsters" but in different ways. Bulgasal is a story of revenge and realisation meanwhile The Guest concentrates more on the horror aspect.

Both have the main theme of a "frame job" which leads the male lead to investigate against all odds and ultimately the real criminal gets punished.

Even though both deal with terrorism and the concept of race against time, Emergency Declaration has a more linear narrative unlike Decibel.

Both the series feature at least one of the main lead who have passed away and explore the concept of void left by their departure. Choco Milk Shake has a lighter tone though.

There is a crazy psychopathic male lead in both and they suffer from similar fates at the end of the series/movie.

Both deal with similar themes of identical faces appearing. The plot remains shrouded in mystery and suspense. Duel is more of a detective story, trying to find out the truth behind the unusual events.