Kii

Kii (キー, Kī) is a Dryad who appeared after being rescued from an illegal extraspecies trafficking operation. When Papi found her, she named her Kii, since Papi stated "she looks like a tree (木, Ki)", she made friends with Papi when she rescued her, and planted her in a forest that just happened to be an illegal waste dump. She has since become friends with Suu and tolerates the presence of humans like Kimihito Kurusu.

Appearance
Kii's appearance changes based on the amount of nutrients she absorbs from soil, but no matter what her hair seems to be made of leaves, and her arms and legs are plant like appendages that look like wood. When she is lacking nutrients Kii appears as a young girl shorter than Papi. In this form she can be very easily mistaken for a child. When she has proper nutrients Kii's true form is that of a buxom adult female of average height. Her breasts were also much larger and implied to be grown bigger if filled with the chemicals. If she keeps on absorbing nutrients in this form it can give the appearance that she is gaining weight.

Because she does not wear clothing Kii uses leaves and vines around her body in order to hide her nudity.

After absorbing experimental chemicals, Kii underwent a drastic change. She transformed into a gigantic tree like plant-monster, with her former adult body located inside the head. Luckily because of intervention of Papi, Suu, and Kimihito she was able to return to her child form, and eventually her true adult form.

Personality
Like Rachnera Arachnera, Kii has severe misanthropic issues due to her past dealings with humans.

When she was planted by Papi near an illegal dumping ground for a prototype super fertilizer, her hatred and anger towards humanity was also increased along with her size. Upon returning to normal, she realized that not all humans were bad, but was still distrusting of Kimihito, if only for the actions he took to remove the nutrients out of her body. Although, her younger form did say he sucked her breasts "nice and gently."

While Kii has developed a certain tolerance towards Kimihito over time, she still shows herself distanced towards others, although this is more a general characteristic of Dryads than a personal characteristic. Kii is always concerned with protecting the forest, but in doing so she can also tend to neglect her own safety when trying to prevent Polt from clearing the litter as too much activity would damage the forest even more, although she was very weak herself.

Skills and Traits

 * Botany: As she is part plant and lives naturally in the environment, she is knowledgeable on all of the matters in nature around her, such as where certain plants grow. However, she lacks certain knowledge such as whether certain plants are poisonous when ingested.
 * Professional Poker Player: As shown in Monster Musume: Monster Girls on the Job!, Kii is a professional poker player and quickly mastered the rules. As Kii explains, however, she is not interested in poker (or any other human game), but plays because she can ruin humans financially. During his time in Polts's casino, Kimihito lost every game against Kii, although it should be noted that Kimihito was a novice and knew little about the rules of poker.
 * Dryad Physiology
 * Nutrient Absorption: As she is half plant, her basic sustenance is water and nutrients from the ground, by placing her roots into the ground. It also affects her in the same way it would a plant, so when she absorbs the experimental fertiliser, she grows to a giant size.
 * Vines: She can use her vines to grab and restrain her opponents.
 * Nutrient Extraction: If required, it is possible to extract the nutrients she has absorbed by sucking on her breasts.
 * Leg Transformation: As is explained in Monster Musume: Monster Girls on the Job!, Kii can transform her lower half. Usually she has roots, but she can form them into two bipedal legs like a human, although they are still covered in bark.
 * Illiteracy: Having lived outside of human or any other extraspecies society, she is unable to write. Her reading skills have not been seen.

Plot
Sometime before her first appearance in the story, Kii and two other extraspecies children were kidnapped and illegally trafficked until they were rescued by both MON and the Cultural Exchange Security Squad. However, she was accidentally left behind by Ms. Smith when the traffickers were apprehended after their truck crashed, leaving Kii lost among the wreckage.

She was eventually found and planted in the mountains near an illegal dumping ground by Papi (who soon forgot about her). After absorbing experimental chemicals, she underwent a drastic change, transforming into a gigantic plant-monster as a result and attacked any human's she encountered.

When Papi returned to the mountains with Suu and Kimihito in attempt to draw out whoever D was, Kii attacked the group with the goals of capturing Papi and causing harm to Kimihito. Finding out Kii was a Dryad the group assumed she was indeed the mysterious "D". During her attack, Kii accidently knocked Suu into a vat of experimental super fertilizer, causing the slime to grow to the size of Kii's plant-monster form. After fighting a bit Suu suggested trying to remove the chemicals from Kii that had turned her into a monster. Papi attempted to do this by sucking on Kii's breasts. When Kii stopped her (using a combination of vines and bondage), Suu made Kimihito attempt the same thing. As a last effort Kii tried sucking the super fertilizer out of Suu. This ultimately resulted in all three girls present reach orgasms and return to their normal size. When Smith arrived to go over the situation she revealed Kii was unable to write and thus could not have written the death threat sent by D. Smith then offered to return Kii to her homeland, or to let her stay in the forest as its "guardian". As they were leaving, Kii asked why Papi and Suu loved Kimihito so much to which they responded "because he's nice." Kii partly agreed with the statement saying the way he had sucked her breast did feel good, earning a humorous reaction from Smith.

After regaining her adult body, Kii would be visited by Kimihito and Suu again when the Kurusu household was low on food. Initially Kii refused to let the two take any edible plants from the forest, but changed her mind after being sexually assaulted by Suu. Kii led the slime and the human to an area with plants that were ripe enough for eating, but was unable to tell them which plants were poisonous to non-plant beings. When Suu revealed she could tell the difference Kii remarked that she was amazed at the slime's useful abilities. After harvesting many plants Kimihito apologized to Kii for taking more than intended, but the Dryad acquiesced to their actions as what they had taken was a small amount compared to what the forest contained. As Suu and Kimihito left, Kii asked Suu to come visit her with Papi next time so the three could play together. When Kimihito told her that was a great idea Kii quickly told him he was not invited to return to her forest. At that point Smith arrived to talk to Kii about getting a new host family, however the dryad was not interested, as she preferred the forest.

Even with all the effort Smith and the Cultural Exchange Security Squad put into cleaning the forest, the amount of trash spread throughout the woods by Kii and Suu's giant monster battle had a negative affect on Kii, causing her to wither and once again revert to her child form. Seeing an opportunity for extraspecies cooperation, the Kobold race decided to take matters into their own hands and clean up the forest themselves, with Polt leading the efforts because of her past interactions with Kii as her probation officer. When scouting where all the dump sites were Kii and Polt came upon Kimihito and Tio having a picnic. When Polt excitedly explained the situation Kii responded by tying up the Kobold with vines and expressed her wishes to just be left alone, regardless of whether the trash was making her ill. Tio saw Kii's negative attitude as unacceptable and sat the Dryad in her lap and explained that everyone cared and worried about her and that they were doing their best to help, and asked Kii to take it easy on them. Kii was caught up by Tio's warm personality and agreed much to Kimihito and Polt's shock. Kii spent the rest of the day resting with Tio while Polt and Kimihito cleaned, becoming slightly agitated when Polt began napping on Tio's lap when she wanted to. Later when Tio started to help clean the group accidentally uncovered a dormant geyser and turned a portion of the forest into a hot springs. This proved to be beneficial to Kii as her species is native to a more warm and humid climate, and the warm waters of the springs caused her to refoliate. When Polt asked to build an Onsen resort at the springs Kii refused stating the construction would disrupt the forest, later she would make fun of Kimihito when he fainted in the springs, calling him a baby. When she encountered Kimihito and Cerea, who were on the run from Kiira, she noticed Kimihito sucking on Cerea's breasts, trying to extract Kiira's venom from them. She questioned whether or not sucking breasts was his hobby, reminding him he had done the same thing to her before, and was suspicious of him wanting to do the same to Tio at the hot springs. She later allowed Kimihito to use the new sauna in her forest to trap Kiira. She approved of it temporarily as long as no trees in her forest were harmed and the trash was all gone.

Zoological Information
Dryads are a type of plant-like non-human species. Their qualities are similar to those of small or medium sized trees or vines.

Though they are easygoing and mild-mannered, they tend to not associate with other species (this is true of all plant-like species).

However, exceptions are made for those who do not harm them or provide them with care, and they sometimes open their hearts to helpful members of other species.

The humanoid parts of their body change according to the amount of nutrients and water they have absorbed regardless of their actual age, making it impossible to determine their age by appearance alone.

Additionally, plant-like species do not wear clothing.

Trivia

 * Like Draco when she began attacking Kurusu, she was suspected of being D but at the end was removed of suspicion due to being unable to write.
 * Her giant form appears to be based on the forest god from Hellboy II: The Golden Army.
 * As a Dryad, Kii would count as the first Elemental/Fae monster to be revealed.
 * Currently she seems to be somewhat more comfortable with being around Kurusu as she let him pick fruits from the forest without complaint and said he could do so again due to the forest having plenty to spare. This could suggest that she's starting to acknowledge him.
 * MonMusu Anime Twitter account revealed that her Birthday is May 4th (May 4th in Japan is Greenery Day).
 * Although Kii was kidnapped and smuggled into Japan against her will, she is still considered an illegal immigrant under Japanese law. This is one of the reasons she leads a secret life in the mountains, hidden from human society, since interacting with humanity only ever made her situation worse (as Kimihito explains in Monster Musume: Monster Girls on the Job!)