Also known as SP, Sanity Points are one of the most important stats in the Shadow Hearts series.
As the name implies SP is a measure of a character's sanity during battle. The SP varies for each character, some may have a naturally low amount while others will be rather high.
Narratively it's a reflection of the stresses of battling preternatural entities - with characters that have long experience of the supernatural (Yuri, Keith, Joachim, etc) having a higher base SP stat, than those who have had little such interaction (Alice, Karin, Johnny, etc).
Should SP reach 0 during battle, that person will go into the Berserk status. Under this status, characters will behave erratically and will possibly attack the allies of their own party.
SP is restored to full after every battle, but can be restored in-battle by the use of Pure leaves, Pure seeds, Pure roots, and Pure Extract - in-universe, a plant-based sedative to calm the nerves.
In the first Shadow Hearts, there are additional items that can restore SP; Alchemist's Water, Eye of Ouroboros, Priest's Wine, Talisman of Power, Talisman of Purity, and Witch's Broth.
Additionally, when Beserk, Anne's Cross and the Blood Jewel can enable SP recovery.
Various abilities and equipment can also alter base SP amounts; Dark Angel earrings increase base SP by 20%. The Huge Jug and Small Jug, halve and double the SP loss per turn, respectively.
A special accessory for Fusionists called the Flare Brooch, can halve the SP cost for Fusion. The Will Power will prevent SP Lowering attacks.
Also the notible abilities of Lucia's Aromatherapy, Tarot Cards and Ricardo's Serenata can effect a character's SP values.