Running away. Getting stabbed and bleeding to death is also a valid option. I’m being a bit of a smart ass here, but this is not a good situation to be in.
In competent hands, a sword can keep your character from getting close enough to actually harm their foe. Even in incompetent hands, it can easily debilitate your character.
For an unarmed character, they need to be able to stay out of the sword’s reach, or get too close to use the sword effectively. Without weapons, even improvised ones, once the character with the sword is ready, this just isn’t possible.
So, your character needs to close the distance before the other character draws their weapon, or run.
All of those martial artists blocking, parrying, and catching swords with their bare hands? Those are exhibition techniques. They look really cool, but trying to use them in a fight will only result in death and dismemberment.
In the past we’ve said there’s no unarmed technique for dealing with a sword, but this is an exception. If your character is wearing plate gauntlets, with articulated, metal grips, (or, better yet, full heavy armor), there is an option to grab an opponent’s blade. So, your character in full plate might be able to deal with someone armed with a sword.
So, yeah, run away or get creative.