>>281527103
>Is this that Sanda manga?
Yes
>What's the plot exactly?
A high school student happens to be an extended relative to Santa Claus and transforms into him against his will for one reason or another. She has a vendetta against Sanda(Santa) and tries to lure him out to do battle.
>She has a crush on Santa Claus?
No(?), but the mangaka has a fixation on old men.

It's also very difficult finding all the chapters to get a full grasp of the story.
Also, it might be lowkey yuri.