Why do they pair the 4 kings/generals up with the 4 inner senshi/scouts?
They tend to do this for 3 reasons. The first is a picture of the four kings/generals hugging onto one the senshi/scouts (the picture can be found on the image page) the creator painted. The second reason is a scene from the Sailor V manga (which predates Sailor Moon and follows the exploits of Venus) in which one of the villains, Ace, tells her that he loved her during the Silver Millennium but she only ever had eyes for Kunzite/Malachite. The third reason is a scene from the 1st volume of the Sailor Moon manga in which Jaedite seems to remember Mars from a long time ago, though he can never pinpoint when. (there is also an interesting section in manga 11 in which Zoisite forces Rei to remember her first flame, whose face is later superimposed with Jaedite’s, making me think that he was Jaedite.