Let's be fair and if you picked reincarnation, you'll remain human unlike Rimuru. For example, I would be reincarnated in the Armed Nation of Dwargon and my Unique Skill is Wuxia (武俠, meaning "martial heroes"), which matches my wish to become powerful enough to survive against the odds. As for its abilities and effects...
Physical Increase: The user's strength, speed, resilience and other physical-based statistics are heavily increased in power.
Sixth Sense: The user's ''danger sense'' is amplified, allowing it to sense incoming/hidden threats within a certain range. When combined with the Magic Sense skill, it this ability becomes even stronger, potentially seeing a few seconds into the future.
Pressure Point Detection: The user can find the pressure/weak points of a target (Visualizing them as bright dots over the points' locations) and strike them to deliver great damage.
Cloud Step: The user's leaping ability is heavily increased, allowing it to cover long distances with a single jump and safely land without harm as long it can land on its feet.
What do you think? What's your Unique Skill?