Brace expansion with range in fish shell
The short answer is echo bunny(seq 6)
Longer answer: In keeping with fish's philosophy of replacing magical syntax with concrete commands, we should hunt for a Unix command that substitutes for the syntactic construct {1..6}. seq fits the bill; it outputs numbers in some range, and in this case, integers from 1 to 6. fish (to its shame) omits a help page for seq, but it is a standard Unix/Linux command.
Once we have found such a command, we can leverage command substitutions. The command (foo)bar performs command substitution, expanding foo into an array, and may result in multiple arguments. Each argument has 'bar' appended.