The Miko

Most clerics swear their lives to the devotion and evangelism of a single god. Be it preparing the rites, administering the sacraments, or standing proud in battle with their holy symbol proudly emblazoned. And while the miko performs all of these duties themselves, they differ in that instead of venerating a single divine entity and serving as their representative on the Prime Material Plane, the miko elect to serve a numerous host of sacred spirits know collectively as the Kami. And while these kami are not gods in the traditional sense, they are still in fact the divine and sacred aspects of all things existing on the Prime plane, and as such require specialized servants of their own to mediate and intercede between themselves and the humans who venerate them. They prepare the rituals. They purify both people and sacred places. They appease the kami when mortals cannot. And in return, miko are granted a far more intimate connection to their divine patrons than many other clerics experience. 

Miko ride the line between clerics and druids: they have a strong connection to the natural world, as revealed to them by the kami they venerate. They are able to heal, to remain vigilant in the face of danger, to restore vitality in the most trying of circumstances, and eventually able to summon those kami they serve onto the Prime Material plane to act alongside them in battle. Unlike other clerics, however, the miko's connection to their kami is deeper and more intimate- the miko often knows and refers to their kami by name, or by the title "kami-sama," indicating respect for the spirit on a personal level not often found with other clerics. Rather than rely on divine intervention and prayers to the holy aspect, miko are more comfortable invoking their kami's names and even forms on the Prime plane when in need of intercession. Miko are experts in the rites and rituals of their chosen paths, and are looked upon as ritual and community leaders by their homelands, either by performing the sacred rites regularly, or by speaking directly with the various lesser kami that live in and around all human settlements. Some miko maintain temples and shrines, while others travel and hold regular matsuri- festivals- in far flung villages where they can invoke the local kami safely. But regardless of the path the miko walks, they all share the same core tenets: purity, connection, and intercession. Purity, to keep the mind and body whole; Connection, to maintain a working relationship with the kami at all times; Intercession, to speak on the behalf of not just the kami, but the humans who interact with them daily. 

Miko fall under two main paths, and choose a specific one when they start their journey. This path determines their specialized training, and how they elect to interact with the kami as a whole. Once starting down a path, the miko cannot change it later on, owing to the devotion they have sworn to a specific set of kami at the outset of their lives as miko. 
Ritualists are community spiritual leaders, not unlike most clerics. They maintain the temple/shrine of their home villages/cities, perform holy sacraments on specifically appointed days, perform ablutions and purifications for local adherents, and are responsible for maintaining the formal lore and history of the local kami. Because of this, Ritualists are mostly servants of the amatsukami, or the Heavenly court of kami, who live in the Celestial realms and are not too different than the major gods of the pantheons. Likewise they maintain more distance with the people who venerate them, and often require far more formalized contact from their miko.
Shaman are often (but not always) wandering miko who choose to interact with "wilder" sacred spirits, or serve as ritual leaders among small villages and towns that might lack a Ritualist to maintain their shrines, or even a major shrine to begin with. Shaman are known for their connections to folk practice versus formal rites, and as such are more adept and adapted to dealings with the kunitsukami, or the kami of the Earthly courts. These kami are more akin to fey or elemental princes, and as such are more unpredictable, but also easier to communicate with and appease via festivals or local offerings. 

Domain Spells

The Miko gains the following domain spells at the cleric levels noted below. Once you gain a domain spell, you always have it prepared, and it doesn’t count against the number of spells you can prepare each day.

If you have a domain spell that doesn’t appear on the cleric spell list, the spell is nonetheless a cleric spell for you. Additionally, while each level contains one static Domain spell, the path selected as a miko presents different options for a second domain spell per level, as noted below. 

1: Protection from Evil and Good; Ceremony (Ritualist), Purify Food and Drink (Shaman)

3: Lesser Restoration; Augury (Ritualist), Animal Messenger (Shaman)

5: Spirit Guardians; Remove Curse (Ritualist), Summon Fey (Shaman)

7: Summon Elemental; Aura of Purity (Ritualist), Guardian of Faith (Shaman)

9: Dispel Evil and Good; Summon Celestial (Ritualist), Greater Restoration (Shaman)

Bonus Proficiencies

At level 1, the miko chooses a specific path they will follow on their spiritual journey: Ritualist, or Shaman. Ritualists gain proficiency in the Religion Skill and Celestial Language. Shaman gain proficiency in the Nature Skill and Primordial Language. If the miko already has proficiency the skill of their chosen path, they instead double their proficiency bonus when making checks with that skill.

Resilient Mind

Dealing with the occasionally unpredictable behavior of the kami has taught the miko to strengthen their own resolve when handling the core tasks associated with their chosen path.

Ritualist: You are so versed in maintaining order during the ceremonies of your Kami that performing them is second-nature to you. When you would cast a prepared cleric spell as a ritual, you can use the spell's normal casting time, rather than adding 10 minutes to it. Once you use this benefit, you can't do so again until you finish a long rest.

Shaman: Your time among the kami of nature has strengthened your mind against their wiles and inclement effects. When you would make a saving throw to maintain concentration, you may use your reaction to add a bonus to that roll equal to your Wisdom modifier, potentially turning a failure into a success. You may use this ability a number of times equal to your proficiency bonus, and regain all expended uses after a long rest.

Channel Divinity: Guidance of the Kami

The miko channels their connection to the kami to grant one of the following effects based on their chosen path:

Ritualist: When you or a creature within 60 feet of you makes an ability or skill check, you can use your reaction to grant that creature a bonus to the roll equal to half your cleric level (rounded up), using your Channel Divinity. You make this choice after you see the roll, but before the DM says whether the check succeeds or fails.

Shaman: When you or a creature within 60 feet of you hit with an attack, you may add a bonus to damage equal to half your cleric level + Wisdom modifier as a reaction using your Channel Divinity.

Channel Divinity: Martial Purification

At level 6, as an action, the miko may remove any one condition or one level of exhaustion from target creature. Additionally, the recipient heals for a number equal to half the miko’s level (rounded up) + the miko’s Wisdom modifier.

Empowered Incarnation

At 8th level, your devotion to the kami allows you to incarnate one as a potent ally in combat. Your connection to this kami empowers it beyond the scope of "traditional magic," and grants it boons when it answers the call to fight by your side. Any fey, celestials or elementals created by a Domain spell that you cast gains two benefits:

It appears as an enhanced form of itself: treated the kami though it was summoned with a spell of two levels higher than the spell slot used (to a maximum of 9th level).

The damage from its natural weapons is considered magical for the purpose of overcoming immunity and resistance to nonmagical attacks and damage.

Lore note for DMs and players: the summoned kami's form may be drawn from Japanese mythology (a kitsune or tanuki for a Fey, for example. Or one of the kami of legend drawn from folk or Imperial mythology like Okuninishi-no-kami or Amaterasu-omikami), or be a creation entirely of the player's desire. There is a rich world of folklore and myth to derive these kami from, so don't feel pigeonholed into spell descriptions if you want to express your interests.

Strength of the Kami

At 17th level, as a reward for devoting yourself to your chosen path, your patron kami imbue you with the fortitudes of their associated domains. 

Ritualists are bestowed resistance to radiant, necrotic, and force damage from their celestial hosts.

Shaman are granted resistance to fire, cold, and lightning damage from their terrestrial allies.

Additionally, at this level of experience, your prowess as a miko is as unrivaled as your connection to the kami themselves, and both you and your patrons are further enhanced by it. Any creature you summon with one of your domain spells is further empowered: they gain a +2 to all attack and damage rolls, and extra hit points equal to your cleric level.