Red potion is avaible for 15,000 coins in Buya, Bagai Shop (029/143) and Kugnae, Baegil Shop (196/200) at the alchemists shops. It restores all vita. Each attempt to weave a Magical Net requires a Red potion. You can only carry 2 potions at a time. The Alchemists will only sell 2 potions every 15 minutes.