Shining doesn't feel very keen on having a foal or filly to look after.
He'd much rather have a niece or a nephew.
So, with Twilight being his only sibling,
and the only pony she seems to have a thing for is Flash,
(at least, that's what Shining thinks.)
The captain puts two and two together and comes up with one simple solution.
"PRIVATE! I order you to buck my sister!"
~And to this day, Atlas still regrets ever writing this fan fic~