Nene appears as a small creature that resembles a rodent with light brown fur, wide maroon eyes and a long tail. There are black markings on his eyes and ears, and has a brown diagonal marking on his belly.
His tail, which is also sentient, begins as a blue-green and light brown stripe and ends with a mouth that resembles a binder clip and large white flaps for eyes.
A curious critter with a penchant for large breasts, Nene is often seen near Ellen Kohagura or any well-endowed girl. He also tends to leap towards the nearest pair of breasts that interest him, much to Kaoru's chagrin. Nene can also somehow communicate with Kaoru, but is limited to muttering the syllable "ne!".
On the other hand, Nene's tail has been depicted as a gruff character who rambles in Kansai dialect.
As the guardian beast of the Mashiko family, he is passed down to notable Toji in the family, the latest of which is Kaoru Mashiko. Kaoru initially did not like Nene because of his nature as an Aradama. However, one day when she was lost in the forest due to an accident, Nene was the one who consoled her and brought her back home. Since then, Nene and Kaoru became an inseparable pair.
Nene is also connected to the folk tale of the Nenekirimaru, the sword that was said to have come alive upon seeing a youkai named "Nene". Apparently, the youkai, which is Nene himself, survived the attack.
Nene is first seen with Ellen and Kaoru when the remaining participants of the National Swordsmanship Tournament were allowed to make their journeys back to their respective schools. During this time, the two students from Osafune Girls' Academy planned an untimely visit to Shonan Beach, and Kaoru had to stop Nene from jumping into Mai Yanase's breasts.
When Ellen and Kaoru were redeployed to Ebisu to catch Kanami Etou and Hiyori Juujou, Nene was also present, although after a short battle between the two parties, Nene showed a friendly attitude towards Kanami while Hiyori was scoffed at for lacking bust size. Later, Nene would be the first to detect a large amount of Aradama nearby, prompting the four Toji to prepare for an offensive. Nene and Kaoru would be isolated from the others, with the pair having to fend off the Aradama swarms alone. Nene eventually shielded Kaoru from harm, injuring himself in the process. Nene's sacrifice would later compel Kaoru to fight more seriously against Elite Guard Yomi Satsuki, the source of the Aradama swarm.
Invisibility: When his presence is not necessary, Nene cloaks his presence, allowing himself to turn invisible at will.
Limited Flight: Nene can fly up to a height of a few feet from the ground.
Immense Strength: Nene has demonstrated the ability to catch Kaoru's sword Nenekirimaru in mid-air, albeit with difficulty, and he can carry the combined weight of Kaoru and her okatana by using his mouth.
Bust Size Prediction: According to Kaoru, Nene has the unusual ability to predict if a girl's breasts would grow in the future.
Aradama Detection: Nene has shown to have ability to detect presense of others Aradama
- Nene resembles a miniature version of a nue, a chimeric creature from Japanese folklore.
- Despite being an Aradama, Nene does not register in Hiyori's Analog Spectrum Meter and the newer Spectrum Sensors. This suggests that Nene is an Aradama with a different composition than the hostile Aradama that are composed of Noro.
- Nene's voice actress, Satsumi Matsuda, is the twin sister of Kaoru Mashiko's voice actress, Risae Matsuda.
- Although the Toji no Tomo 4-koma series depicts Nene's tail as a vocal character distinguishable from the body, the anime production team decided to not give the tail any speaking lines in the story.