Skill: Quickness
Initiative was a time honored psuedoskill that had whole traits, trees, and talents dedicated to it. In CHASE, it has become a fully fledged Primary Skill in its own right, dictating not only one's speed, but one's ability to jump into action or maintain speed due to peak endurance. To this end, Quickness and its various talents are governed by both Dexterity and Constitution. Quickness also governs one's ability to counter being overwhelmed by others who would rely on surprise and the like.
Mechanically, when rolling for Initiative (for both Combat and Exploration), a creature will use their Quickness stat, even untrained.
Quickness uses DEX / Dexterity or CON / Constitution by default. Quickness is a Primary Skill, meaning it is a major skill that can only be gained by mechanics that grant proficiency.