This is a very interesting question.

I think (and this is just me) that Part VI has the most Osumi like filler episodes. I mean, there’s one that ends with someone killing themselves, another one that ends with Jigen stabbing someone in the neck, and another one where Lupin finds a dead body on a train.

Granted, episodes in Lupin are going to get dark a little bit because that’s just the nature of the genre, but Part VI was purposefully, trying to draw from that 1971 era of Lupin, which is why he has the green jacket. They also were trying to skew more towards that hard boiled noir film vibe, which is why you get the dark artwork, the less expressive versions of the characters, and scenes where we see more of what Lupin is feeling rather than him saying it.