Priest

Summary
The Priest (僧侶 / Sōryo) is one of the starting classes in DQX and primarily focuses on healing. With access to a wide range of status curing and HP restoration spells, as well as a few buffing spells, it is the best class for a pure support role. Its buffing abilities are not as great as that of some other support classes such as the Minstrel or the Dancer, but it makes up for it by having extremely high magical mending-- it's the archetypal healing specialist class. They are capable of using Wands, Spears, Staves, and Shields, in addition to access to the class-exclusive skill tree Faith (しんこう心 / Shinkō kokoro).

Strategy
In battle, Priests should almost always be playing a support role. They have very few capabilities when it comes to damage output-- they can equip staves or spears for better results but this will inevitably be detrimental in any kind of difficult content since it will take away from the defense and magical mending boon provided by the traditional wand and shield combination. In combat, a Priest's role should generally be staying away from enemies and making sure the party is taken care of. Healing should be top priority, and applying buffs should be next. Only when the necessary buffs are applied and your party is at full health can you focus on things like damaging or debuffing enemies. In terms of character/equipment build, Priests should prioritize HP above other stats as they naturally have low HP and keeping the healer alive is one of the most important parts of combat. Defense should come next, and then Magical Mending third (this is an important stat but normally the character won't need to be built to prioritize it as this class's magical mending is naturally very high), and the others can be up to your own discretion.

Priests have a special class-specific skill called 聖なる祈り / Seinaru inori (Care Prayer) which allows them to double their magical mending. This is an extremely useful ability and is one of the primary reasons Priests are quintessential to so many party formations. One of the first actions you should take at the beginning of any difficult battle is to make sure this buff is applied. Another important self-buff is the 天使の守り / Tenshi no mori (Grace of the Goddess) skill, which lasts until you die, where it will auto-revive you at 50% HP. However, this buff takes longer to cast and shouldn't be prioritized over healing a party member. ラピッドステッキ (Rapid Stick), a Wand skill, will reduce spellcasting time by 50% for one minute after use, but it does take time to recharge. 聖女の守り / Seijo no mori (Alma Mater) is important to apply to both allies and the self, as it will protect one time against an instant death attack (leaving the character at 1 HP), as long as the initial HP is over 50%. 女神の祝福 / Megami no shukufuku (Divine Intervention) does the same thing but allows the character to survive the deathblow *regardless* of initial HP. This skill, however, does take time to charge. The last "quintessential" skill (not necessarily required, but is useful in most battles) is キラキラポーン / Kirakirapōn (Snap, Crackle, Poof), another wand skill, which will give any party member immunity to receiving negative status effects while the buff is in place.

A recommended flow for battle is to set up Care Prayer and Rapid Stick as soon as possible, but prioritize these behind immediately necessary healing. Once you have these set up you can apply group buffs like Kabuff (スクルト) or Insulatle (フバーハ) depending on the strengths of the enemy. If there is a more immediate threat of death then Alma Mater (on the one or two allies that need to stay alive) may be a better option. Multiheal (ベホマラー) is going to be your primary tool for healing, although for individual allies-- and depending on their remaining HP, Midheal (ベホイミ) or Moreheal (べホイム) will also be necessary. Priests actually technically have access to Fullheal (ベホマ) as a spell with charge time, although there are practically no situations in which it is ever necessary because Priests have naturally high enough magical mending that Moreheal will almost always be strong enough to restore any one ally to full HP.