If You Take the Enemy Prince as a Knight

"Be my sword."
Sasha, sixth princess of an empire, preparing a coup against her own tyrant father.
Sasha encounters Regen — a captive prince of an enemy nation, and her first love — and offers him a bargain he cannot refuse.
She will restore his power. In exchange, he will swear himself to her as her sworn knight.
He will stand with her through the Imperial Trial — the succession contest she must survive if she means to live past a mad tyrant bent on killing his own daughters.
"Sasha saved my life. I don't know how I'm meant to repay that."
"There's no need to repay it."
"Why not?"
Live. Just stay beside me. That alone is fierce enough.
But she can't let a love that's still very much alive show on her face —
so she sold him a lie about one of her sixty-seven dead brothers.
"It's because you… resemble the brother I lost."
---
"Shall I take it off for you?"
Thinking it over, this seems right.
It's my responsibility to confirm — shouldn't it cost me some effort, with my own hands?
"…Ha. Sasha."
Regen let out something long — a sigh, or something closer to a groan, she couldn't tell which.
He looked at her without a word, then suddenly pressed his lips to her crystal glass on the table.
A murmur, threaded through with doubt, brushed against her ear.
"This is supposed to be non-alcoholic."