Kodama Nezumi 小玉鼠

Tiny fey (spirit), unaligned

Armor Class 15 (preternatural hide)

Hit Points 18 (4d4 + 8)

Speed 20 ft., burrow 10 ft.

STR 2 (−4) · DEX 17 (+3) · CON 14 (+2) · INT 6 (−2) · WIS 14 (+2) · CHA 10 (+0)

Saving Throws Dex +5, Wis +4

Skills Perception +4, Stealth +7

Damage Resistances bludgeoning, piercing, and slashing from non-magical attacks

Damage Immunities cold, poison

Condition Immunities frightened, poisoned, prone

Senses darkvision 60 ft., passive Perception 14

Languages understands Common and Sylvan but can’t speak

Challenge 1/2 (100 XP)

Traits

Forest Camouflage. The kodama nezumi has advantage on Dexterity (Stealth) checks made to hide in snow, leaf litter, or underbrush.

Sound-Triggered Doom. If a thunderous noise (such as a weapon attack, the thunderwave spell, a creature shouting, or any noise audible from 100 feet away) occurs within 60 feet of the kodama nezumi, it must use its Reaction to Bound and Burst.

Bound in Silence. While the area within 60 feet of the kodama nezumi is under the effect of a silence spell or similar magic that blocks sound, it is incapacitated and can’t use Sound-Triggered Doom.

Actions

Nip. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 5 (1d4 + 3) piercing damage. (The mouse uses this only if cornered.)

Bound and Burst (Recharge 4–6). The kodama nezumi springs up to 60 feet in a straight line without provoking opportunity attacks and detonates in a spray of spectral gore. Each creature within 10 feet of the chosen space must make a DC 13 Dexterity saving throw, taking 9 (2d8) necrotic damage on a failed save, or half as much on a successful one. Creatures that take any damage are Cursed by Mountain Misfortune (see below). The kodama nezumi is destroyed when it bursts.

Cursed by Mountain Misfortune. A cursed creature has disadvantage on its first attack roll, saving throw, or ability check each turn. At the end of each long rest, the creature can attempt a DC 13 Wisdom saving throw; on a success, the curse ends. The curse can also be ended by remove curse (PHB p. 271 / 312) or comparable magic, or by presenting an offering worth at least 10 gp at a sacred mountain shrine.

Reactions

Bound and Burst. (See above, triggered by Sound-Triggered Doom.)

Lore

A mouse spirit living in the hollows of ancient trees, keeper of the forest’s secrets.

Kodama nezumi is a yokai of north-eastern Japan whose name is written 小玉鼠 and literally reads “little ball mouse.” The compound uses the characters for “small,” “sphere,” and “mouse,” and it points directly to the creature’s appearance: a tiny rodent curled into a perfect globe, much like a hibernating Japanese dormouse—an uncommon forest dormouse that hunters sometimes find in winter as a hard lump. Yet in Matagi folklore this harmless sleeper has become a messenger of a curse. People say that in this spherical form lie the souls of hunters whom the mountain goddess Yama-no-Kami has trapped there. The legend tells of two hunting companies. One day a young woman, exhausted from the road, asked the hunters of the “Kodama school” for food and shelter so she could regain her strength, but they mistook the goddess for a vagrant and drove her away. She then turned to the hunters of the “Aoba school,” who offered her roof and food. Later everyone discovered that the woman had been Yama-no-Kami herself: the first group, for their ignorance and insults, she cursed—turning them into kodama mice—while the second she blessed with good fortune. Hence the yokai’s very name, directly linked to the name of the offending party.

The creature’s appearance is deceptively harmless: palm-sized, covered in thick whitish fur that blends perfectly with snow. It sports no fantastical features like horns or wings, so a chance encounter stirs no alarm. Danger shows itself only when the sacred silence of the mountains is broken. The instant it hears a loud noise—especially a gunshot—the kodama nezumi moves toward the source; some tales describe this as a supernatural bound, almost teleportation through deep drifts. Once it reaches the target, the rodent suddenly swells until it hits a critical size, then explodes with a deafening pop. Blood and entrails spray outward; any droplet that lands on a person lays a curse of misfortune. From that moment the victim is hounded by catastrophic mishaps: misfiring rifles, sudden avalanches, falls from cliffs, ice cracking underfoot. Folklore stresses that the kodama nezumi doesn’t kill directly—it merely triggers a chain of accidents that, in mountain country, almost always ends in death.

From Yokai Bestiary 5E, Book Two, p. 58 · Fern Flower Press