A port of Darius was originally being developed for the Mega Drive, but got cancelled. A fan-made port was being made by a guy who goes by "Hidecade" as a proof-of-concept, until M2 further developed it for inclusion in the Mega Drive Mini/Genesis Mini. You can even choose to fight the bosses in the arcade original or all 26 from the PC Engine ports.
An updated version known as Darius Extra Version was released on physical cartridge, with a limited release. It's like the similar arcade game where you can enable the quirks added in that version.