From Sega Retro
Konami Justifiers are shaped like pistols, but are brightly coloured due to early 90s fears that light guns could lead to gun crime. They are controversial peripherals for other reasons too - namely the fact that they are incompatible with some games reliant on the Sega Menacer. Lethal Enforcers and its sequel are only compatible with Konami Justifiers, so if you're a fan of light-gun games, you need both controllers to play every game in the library.
The Mega Drive supports a maximum of two Justifiers at once - a blue one, which plugs into controller port 1, and a pink one, which plugs into the blue Justifier.
Like the Menacer and most other light-guns of the era, Konami Justifiers rely on scanlines produced by CRT televisions, making them incompatible with modern day LCD, Plasma or LED sets.