The plot revolves around the heroines being told by several animal spirits, that their fellow animal spirits are planning to take over the surface. The heroines along with an animal spirit venture into Hell to take out this potential threat.
The all-too-familiar shrine maiden of the Hakurei Shrine.
Beast spirits had begun to invade from Hell en masse.
A beast spirit that was cooperative with humans told her that it'd lend her its power, so she decided to go to Hell.
She wasn't completely convinced by what the spirit had told her, but she would be more powerful than if she went to Hell by herself, and she could always just defeat the beast spirit itself if things came to that, so she decided that it didn't pose any disadvantage to her.
An ordinary magician living in Gensokyo. She has a mania for collecting things.
By allowing a beast spirit to possess her, she could become far more powerful than usual.
As this was an extremely attractive prospect to her, she took the beast spirit up on its offer.
She felt no fear about going to Hell. In fact, she was quite excited to find out what sort of beings awaited her.
The gardener of the Netherworld. A bit scatterbrained.
She received a report that beast spirits were invading from Hell, and set out to investigate.
The covetous beast spirits planned to devour every last body on the surface world, both physical and spiritual alike.
If left alone, they would turn the surface world into a hellish world where the strong feast upon the weak.
Who was sending Hell's beast spirits out to attack? Why were they doing it?
The only way to know was to venture into Hell and find out.
A master at skillfully stacking stones.
Her stone-stacking technique is superb, and she serves as a sort of leader of the spirits of stillborn children at the Sai no Kawara.
She's also a god of fortune who's able to change simple, pointless work into something that's enjoyable and worth doing, and who can make the best out of any bad situation.
Her ever-cheery demeanor, bright intellect, and penchant for constantly holding exciting new events like stone-stacking contests makes her the Sai no Kawara's resident idol, beloved by all the children's spirits there.
She's utterly furious with the protagonists for ruining the latest stone-stacking contest, but actually, it was mostly the fault of the beast spirits who arrived from Hell.
A fearsome oni who drags living creatures beneath the Sanzu River's waves.
She carries a stone carving of a baby. Once she gives the baby to someone to hold, she makes it heavier and submerges them in the river. She was an awe-inspiring youkai who took advantage of humans' kindness.
However, since she's forbidden to attack humans in Gensokyo, she currently runs a fishery at the Sanzu River.
If one tries to cross the river without a shinigami's permission, they'll be attacked by creatures like extinct giant fish and plesiosaurs. Nowadays, she spends her time domesticating those giant fish and makes a living wage by sometimes selling them in Gensokyo.
Some youkai view this defanged state of hers as deserving of mockery, but she's quite proud of her current life.
Occasionally, she also guides those who mistakenly attempt to cross the Sanzu River back to their original world.
The guard of the checkpoint leading to various Otherworlds, such as Hell and the land of oni.
Her job is to distinguish betwen humans and oni, and sort them into their respective locations.
In her appearance here, the yama have informed her of a human who wanted to enter Hell, but she was worried about how the human would fare in Hell, so she decided to test their strength.
Her place of work is at Higan, but she doesn't spend most of her time there. She seems to typically reside at the top of a waterfall on the Youkai Mountain, in a spot with a beautiful view.
Her true identity is that of Niwatarijin, the god of wild chickens from before they were domesticated. People tend to think of chickens as being sort of weak and cowardly, but she's a polite and just god who values equality and altruism above all.
She's quietly considering what she can do to help raise the status of chickens, who've been reduced to a food source for humans.
Yachie is the head of the Kiketsu Family, one of the four major organizations in the Animal Realm.
She sent the beast spirits to the Human Realm in search of a human who could be of use. She acts courteously towards everyone, but looks down on the vast majority of them.
Nobody can resist her.
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The Animal Realm, the ultimate survival-of-the-fittest world.
It's a world where the strong rule as they desire... or at least it was, until a few beasts that were just a little more clever and wily than others began to form organizations.
By now, a select handful of gigantic organizations dominate the world. One of these is the Kiketsu Family.
Almost all of the animal spirits already have no chance of victory by themselves, and the only way to survive was to team up with one of these organizations and continue fighting as their slaves forever.
Even as everyone continues to fight to exhaustion, an organization can never be stopped. Within the Animal Realm, each of these enormous beast organizations competed for their share.
Meanwhile, there was one group of spirits that were complete slaves to all of these organizations.
Creatures that were weak in power, but had extremely dexterous hands: homo sapiens. In other words, human spirits.
The human spirits cursed their powerless selves, and began praying to a god.
That god responded by giving the humans idols to worship.
The power of faith was revolutionary.
With their newfound faith, the human spirits no longer feared the beast spirits at all.
Since acting out of anything but selfishness was previously impossible in the Animal Realm, perhaps their newfound ability to act in the spirit of altruism had a large effect on them.
However, it was actually the idols, not the human spirits, that had the power.
The human spirits intended to devote themselves to the divinity beyond the idols, but they actually came to worship the idols themselves.
As a result, it was only natural that these idols began to dominate the humans.
The idols took control of the Primate Spirit Garden, and the status of the human spirits plummeted to the bottom once again.
In being dominated by idols, the Primate Spirit Garden became the most awful, out-of-control organization of all.
The idols flew forth from the Primate Spirit Garden, and began to take over the Animal World.
The idols had no flesh, soul or desire, and so the beasts were quite literally unable to lay a finger on them.
But the beasts weren't simply sitting around and waiting to be dominated, either.
The Kiketsu Family, which specialized in sneak attacks, brought things back from the brink by devising a strategy to overthrow the idols.
Namely: "drag in a human from the surface, and destroy the Primate Spirit Garden with a human's own hands".
Since the beasts were incapable of forming religions of their own, they would invoke a religious war by pitting the idols against a human whose faith was different from the Primate Spirit Garden's idolatry. A truly bold strategy.
Getting to the surface world from the Animal Realm wasn't an easy task.
However, the Animal Realm and Hell are right next door to each other, and are relatively easy to navigate between.
Because Hell was currently going through a power struggle of its own, it was easy to travel through it to get to the Human Realm.
The beast spirits went to the surface via Hell, and put on a show of pretending to invade it (though if they actually succeeded in dominating it, that wouldn't have been half bad either).
The head of the Haniwa Army Corps made by Keiki.
She's skilled in swordsmanship, archery, and equestrianism, and despite her old-fashioned technology, her pure combat prowess is extremely high.
It's been predicted that the workforce of human and animal spirits will be gradually replaced by the more efficient haniwa, because they can be immediately repaired after they've been destroyed, they can't get sick, and they don't need any rest.
Also, because none of the Animal Realm's residents have physical bodies, they quite literally couldn't lay a finger on any of the haniwa, who had physical forms of their own (even if said forms were just idols).
Since spiritual attacks could only affect spiritual bodies, these attacks had almost no effect on the hollow idols.
They usually protected the Primate Spirit Garden, but since they promptly eliminated every potential enemy in the Animal Realm, the soldiers became useless dead weight.
That was when a flesh-and-blood human who could destroy the idols arrived.
A god summoned by the human spirits of the Primate Spirit Garden to pull them back from the brink of disaster.
She is capable of crafting elaborate idols.
The idols she creates are excellent items that can gather faith, act as stand-ins, play with you, and decorate your home.
She took control of the Primate Spirit Garden and extended her protection to the human spirits being treated horribly by the animal spirits.
She believed that they could coexist with the animal spirits as well, if they could come to respect the human spirits.
However, she never thought that the likes of the animal spirits would come up with a plan to bring over a human from the surface to destroy her idols.
Tricking a human into participating in their strategy to wrest control from the human spirits... what a truly beastly act.
The matriarch of the Keiga Family.
When word spread through the Animal Realm that the previously-invincible Keiki of the Primate Spirit Garden had been defeated, she made her next move in a flash.
She thought that with Keiki out of the picture, it'd only be a matter of time before the Animal Realm fell under her own control, so she went to inspect the Human Realm in advance-- and take control of it too, if at all possible.
As soon as she thinks to do something, she does it without a second's hesitation.
Because she values her underlings' opinions and achievements, among other reasons, she's one of the more popular organization heads. (Though all the work she does is unbelievably dirty.)
She likes strong people, even if they're an enemy.
She gets along terribly with both Kicchou and Keiki, but she does respect their strength.