Hoshi no Densetsu Agartha

Remi Tachibana is a girl who adores mysterious phenomena like UFOs - as well as the works of Shotaro Ishimori. One day, while she gushes over UFOs to Ishimori, a young man named Shun Kuroki comes in, wishing to become Ishimori's assistant. Remi and Shun take an immediate liking to each other, and Shun gets accepted. However, a series of strange phenomena begin to occur. Shun also appears to be hiding something as well...

(Source: Kodansha, translated)