When Hidden Blade says 'Kill a unit at a battlefield. its controller draws 2,' does 'its controller' refer to the controller of the killed unit or the controller of the battlefield?

Ruling: 'Its controller' refers to the controller of the killed unit, not the controller of the battlefield.

Nuances:

• The word 'unit' is the subject of the sentence, while 'at a battlefield' is a descriptor, so 'its' grammatically refers back to 'unit'
• If it referred to the battlefield controller, the card would be poorly designed since when played as a hidden reaction during showdown, you would already control the battlefield, making the wording unnecessarily convoluted instead of just saying 'draw 2'