Shizuku is a mizuchi, a water dragon deity, who made a brief appearance in chapter 3 of the manga and is later re-introduced in chapter 5. She assumes the form of a green-haired child with red eyes, looking like a drowning victim just pulled out of the water, abnormally pale, cold to the touch and dripping wet, and has a cold-fish personality to match her appearance. Her demeanor can quickly change to a murderous grin when her desire to kill emerges. She first appears to Yuto at a nearby lake in the forest where Himari was killing other ayakashi, warning him to deviate from his Demon Slayer heritage or face death, and then disappearing. Later on, after witnessing Yuto's resolve to save Himari from her water whirlpool during her fight with the latter, she becomes puzzled about him and, in an attempt to understand him more, invites herself to live in his house, flirting with him on multiple occasions. She is shown to have developed feelings for Yuuto and also tends to show signs of jealousy when another girl flirts with him. Her family was killed by the Jibashiri Family of Demon Slayers 100 years prior to the series' start, and she bears a grudge against them as a result. However, she lets go of it following an intervention from Yuto and Himari after meeting one of their descendants. She often ends her sentences with na no("You know"), and her name is a homonym for a drop (of water).
As a mizuchi, Shizuku can manipulate water and ice and use it as a weapon or a shield, even using it to heal the wounds of others, once doing so with Yuto after Himari's battle with Ageha. However, if the water is mixed, such as with another ayakashi's blood, she cannot control it. She can also regenerate her body after being sliced in two and her hair extends whenever her desire to kill emerges. She is also very sensitive to variations in temperature, as she is cold-blooded, and needs to cool down in the summer by eating shaved ice or other frozen treats and needs to warm up in the winter by staying in warm places (such as hiding in a kotatsu). She can also extend her snake-like tongue to great lengths. She states that her kind were excellent housekeepers prior to the Demon Slayers' arrival, and is very adept at cooking and cleaning as a result.