Not that aggresive already have 3
My female convict tried to bite the eyes out of my upside down catfishes, it almost killed 3 tiger barbs, it forced my firemouth into cowering under the filter for weeks, and even almost killed the male I was trying to get it to breed with. when I tried to keep live plants with her, she ripped all the leaves off of them out of boredom. The only thing I can keep in her tank at this moment which she doesn't rip up, uproot, or knock over is a flower pot.
What kind of fish are you looking for if that's not aggressive enough?
63 litres doesn't give you a lot of room in terms of aggressive fish. IMO, it's too small a single convict. Dwarf puffer fish can be mini monsters, but they are pretty costly to maintain, since they need a steady diet of live shelled foods like shrimp and snails to keep their beaks from overgrowing, and are messy fish, so over-filtration is encouraged. They tend to get bored easily, so it's good to add new decorations now and then to
I think you can keep 2 or three in a 63l tank, but I'd check with somebody who knows more about them. All I know is they're small, predatory, and can't be kept with other species of fish.