Can a player use Hidden Blade from hand to kill their own unit before Temporary destroys it at the start of their beginning phase?

Ruling: Hidden Blade from hand cannot be used to react to the Temporary trigger because it is not a reaction. However, if Hidden Blade were already hidden at the same battlefield, it could be used at reaction speed to kill the temporary unit before the Temporary effect resolves.

Nuances:

• Hidden cards can be played at reaction speed to anything on the chain
• Hidden cards have additional targeting restrictions that must be followed
• You may use reactions to triggers caused by phase changes (like the Temporary trigger being put onto the chain), but cannot take actions before "the start of your beginning phase" otherwise