Natsuki☆Fullswing!

is a Japanese light novel series written by Hideto Kido, with illustrations by Arima Honda. The series began publication on February 10, 2007 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
In front of Tomonori, a high school student who broke his shoulder and quit the baseball club and smoldered, Natsuki, a mysterious woman wielding a metal bat named "Yumema Crush", appeared. It is said that Tomonori is obsessed with Yumema, an entity that shows "dreams" and misleads humans. When Natsuki bites Ketsubat into Tomoki and extinguishes Yumema, she begins to cling to Tomoki in order to infiltrate the place where boys and girls with a high latency rate of Yumema gather. When she opens her mouth, she is vulgar and noisy, and while she is ignorant of Natsuki, who is of unknown age and does not care about people's inconvenience, Tomonori pursues the incubus possessed by people with her.