What it does
Charti Berry triggers automatically when the holder takes super-effective Rock-type damage, halving that hit, then is consumed. Only fires on super-effective Rock moves — neutral or resisted Rock hits leave it alone.
Flying and Fire types can be 4× weak to Rock (both types take ×2 from Rock). In practice, that means Rock moves frequently land as one-shots. The berry turns a 4× hit into a 2× hit, or a 2× hit into neutral — if you have any real bulk, that's often the difference between fainting and surviving.
Vs. Focus Sash: both survive an otherwise-lethal hit at full HP. Focus Sash leaves you at 1 HP and one attack away from fainting regardless. Charti Berry leaves you at actual remaining HP, which may be enough to take another hit.
Who runs it
Volcarona (14% of sets) is the headline user. It has a 4× Rock weakness, and Rock Slide from anything hits it dangerously hard. The berry compresses that to 2×, which is often exactly the margin to fire off a Quiver Dance before you're gone. Talonflame (4%) and Charizard (6%) have the same structural vulnerability, and both are fast enough to act first after surviving. Pangoro (15%) takes a different angle — 2× weak to Rock, but slow, so it runs the berry to absorb a direct hit and guarantee its action. Gyarados (2%), Noivern (2%), Castform (3%), and Emolga (2%) pick it up situationally.
How to use it
Rock Slide is one of the most-used doubles moves in the game — hits both targets, chip flinch chance, and almost any Ground/Rock type carries it. Your Flying-type is on the field, there's a Rock-type threat across from you, Rock Slide is coming. Charti Berry buys you one extra turn of action from inside that danger zone.
The best moment for the berry is the first turn when you'd otherwise die. If you can Protect one turn and the opponent's Rock setter is gone by then, you might never need it. Deciding when to Protect vs. commit is the core decision for any berry carrier.
Tips & strategy
There's a hidden advantage: your opponent doesn't see your item. If they calculate that Rock Slide KOs you and then it doesn't, their plan for that turn falls apart. You got a free action, and they spent resources on a KO that didn't happen. That tempo swing is often worth more than just the HP you kept.