The Duke Needs His Coffee

The protagonist has possessed the body of April, a supporting character who was killed by the male lead after being manipulated by the villain.

She ignores the original storyline and resorts to spending the rest of her life running a café secluded in the countryside, but as the little boy she started to raise by chance turns out to be the nephew the male lead was desperately searching for all along, her resolution begins to go greatly awry.

April becomes the male lead's exclusive barista, and she pours him a coffee imbued with magic every night.
Eventually, she also ends up opening a café in the capital. She's planning to do so until the female lead makes her appearance. And around when that happens, she'll slowly start to leave the male lead's side.

There’s only one problem— she’s starting to grow fond of this life with him.