Dumped After My Engagement: Becoming a Military Noblewoman

The year after Celestia's mother passed away, her father brought home his second wife and her daughter. She was relieved, thinking they could get along, but her step-sister's attitude suddenly changed drastically. "Because I'm the heroine of this world!" While Celestia was still surprised, one after another, numerous words that she couldn't just ignore came spilling out... According to her step-sister, it seems Celestia is destined for a future where her engagement is broken, she is abandoned by her beloved father, she acts disrespectfully towards royalty, and is ruined. She found herself thinking, "Is this a well-crafted delusion?" and was amused, but it seems what her step-sister said might actually be true... To escape this terrifying future, Celestia resolves to quit being a noblewoman! Her first step is to go to her grandfather, who is a military man. However, she ends up enrolling in military school just like that, and by force of circumstance, gets a job as a soldier... Before she knew it, she was promoted to Colonel. Furthermore, the nicknames she ended up with include 'The Brutal King of the Frontier Fortress', 'Battle Maniac', and more. Her colleagues and subordinates are teeming with royalty and nobles. And for some reason, even royalty from countries are trying to join them?! She was supposed to have quit being a noblewoman, but her social circle has clearly become extravagant than before she quit.