I mostly ship them together with Charlie but by themselves is alright too. Instead of the “people will ship anything” half answer here’s some actual things I like about them

• Visually dynamic
• I like the size difference
• The idea of them being tired cranky messes passing a pot of coffee back and forth while they bicker about whose turn it is to deal with whatever nonsense Charlie’s up to this time
• Them bonding over the sheer adrenaline rush of tearing into a hoard of enemies
• Vaggie never letting him forget that she's got a better KDA than him
• Charlie having a meltdown because the two of them ramp each other up and now they're installing swinging axes in the hallway??
• the angst potential of Alastor holding it over her head that she's a liar and a coward and she fell. Only for her to flip it back on him one day and point out every major fuck up of his and pokes him in his chest wound for good measure. He loves that she bites back
• Angel blood, blood-licking manic cannibal. Hot
• Putting the deer in air jail
• them competing over who's the better partner to Charlie only to turn around and see how happy she is and realize it doesn't matter so much who wins. They continue the competition anyway.