Wil is in a dilemma once again.
On one side, his reasoning is telling him to choose Absolute Freeze, the most logical thing to upgrade.
On the other side, something told him to choose the unique skill as a reward. So far, all three unique skills are overpowered in their own way.
Pegasus gives you the ultimate speed. Gravity suppression makes your enemies powerless, and Heavenly push can let him kill anyone from far away.
Just like those three, this unique skill is going to be an awesome one. Call it intuition or whatever.
Wil is someone who hates gambling. That's why he was always skeptical about the quest with unknown rewards. But, the level of difficulty and trust in the old man made him trust his guts.
In the end, he chose the unique over upgrading Absolute Freeze.
*Ding! You selected a unique skill.