Something something Lupin IV time traveling story where he gets stuck in the past with his gang.

Runs into Zenigata while trying to get his dad's attention by posing as him, Zenigata's mind slowly turns it's cogs about it.

Yes it's Mamo related lol (I had a larger summary on the idea I had for fun, basically Lupin IV and his twin with their gang are stuck in the past because Mamo's grandson has some dumb big scheme to try to get Lupin and his own kids kill each other so he can get revenge and end the Lupin line and legacy once and for all.)

Also of course Zenigata catches on he's not Lupin III.