You've trained to gain further access to your Genasi elemental powers, gaining charges equal to your proficiency bonus. When you hit a creature with an Unarmed Strike, you may expend one charge to deal an additional 1d4 damage, with the type of damage determined by your Subrace:

• Fire Genasi - Fire
• Water Genasi - Cold
• Earth Genasi - Acid
• Air Genasi - Force

The damage increases to 2d4 at 7th level, again to 3d4 at 11th level, and to 4d4 at 17th level. You regain all charges on a short or long rest. At the start of your turn, if you have no charges, roll a d6, on a 6 you regain half your charges rounded up.