SPOILER WARNING: The plot is minorly disbelivable in that it hard to believe any army would give Captain status to a 14 year old boy (because that is what our fresh faced heroine looks like) and that his men would just fall in line and respect him just because the Tsar said so. We know that's not human nature. There'd be some men who'd let actions speak, but we know there would likely be more that would accusing him of being the Tsar's pet, or of his family of buying his rank, and they' be disrespectful and trying to discredit him, at least when no one was looking. It just wouldn't be so perfect. That said, it's easy to set that pesky little detail aside and enjoy the story for the most part. I say for the most part, because next I'm left wondering how does a man (as that's what the heroine conducts herself as and has had virtually no training to be a lady) manage to attend a ball and not trip over her heels and skirt and pull off acting like a lady? It should have been nearly impossible unless prior to the first foray 'he` underwent extensive training, and if he did, it wasn't mentioned. It was little things that threw it off for me, but I still enjoyed it... for the most part. And the art itself is worth enjoying.
His Cavalry Lady manga 1
His Reluctant Mistress 2
His Forbidden Liaison 3