Guardian and Protector are a set of Support-class Psynergy aligned with the Mars element featured in both games. Its primary usage is to bolster the defense levels of party members. It is available to the Samurai Class series; thus, the two Venus Adepts Isaac and Felix and the two Mars Adepts Garet and Jenna are able to access this Psynergy.
The Guardian Psynergy series, in function, visuals, and statistics in general, is completely identical to the Guard Psynergy series held by various other class series, so they might as well be treated as the same Psynergy. Since the Jupiter Adepts Ivan and Sheba and the Mercury Adepts Mia and Piers can have access to the Guard Psynergy series, it is as if all eight Adepts can perform this simple defense-bolstering tactic.
Guardian: “Boost Defense with divine might.”: This costs 3 Psynergy Points and affects one party member. Red-white energy gathers into the Adept and a shield image appears above the Adept to signify enhanced defense. The Adept's defense rating is temporarily improved by 25%; in Golden Sun games, a party member's defense can be enhanced up to a maximum of 150% of his or her normal defense rating, so using this twice will cause that Adept to attain 150% defense. It is available at level 3.
Protector: “Boost Defense with divine might.”: This costs 5 Psynergy Points and affects all party members. Red-white energy gathers into all party members and a shield image appears above each party member to signify enhanced defense. All Adepts' defense ratings are improved by 12.5%, so using this four times will cause all Adepts to attain 150% of their normal defense levels temporarily during battle. It is available at level 15.
A fairly staple move within the RPG genre, raising your own defence can be a valuable tactic. However, as most bosses can cast the Break Psynergy, and it only lasts for a short period of time, it is quite possible to have the effect wear off before the enemy attacks the buffed adept, effectively wasting a turn and PP. The defence multiplying effect means this move becomes more valuable as the party progresses, as it buffs the party by a larger absolute value. This can make it useful against bosses that have high attack ratings, though it depends heavily on the situation.