is a Japanese sound symbol word (gitaigo) that essentially represents the "sound" of something sticking out in a flat surface, or the sound of something rising very quickly. A popular term with fans of 1980s Japanese animation, it was popularized in the manga

Manga

Manga is the Japanese word for "comics" and consists of comics and print cartoons . In the West, the term "manga" has been appropriated to refer specifically to comics created in Japan, or by Japanese authors, in the Japanese language and conforming to the style developed in Japan in the late 19th...

 and anime

Anime

is the Japanese abbreviated pronunciation of "animation". The definition sometimes changes depending on the context. In English-speaking countries, the term most commonly refers to Japanese animated cartoons....

 City Hunter

City Hunter

is a hardboiled manga series written and illustrated by Tsukasa Hojo, published by Shueisha in the Weekly Shōnen Jump from 1985 to 1991. The manga was adapted into an animated television series by Sunrise Studios in 1987...

 by Tsukasa Hojo

Tsukasa Hojo

is a Japanese manga artist. He studied technical design while still at Kyushu Sangyo University, where he began to draw manga. He worked on several one-shot stories before releasing his serialized works: Cat's Eye, City Hunter and Angel Heart....

. Ryo Saeba, the main character of City Hunter, took jobs to help people in need, always on the lookout for a "mokkori chance" (in the context of the series, a chance to do something perverted with an attractive woman, such as groping her buttocks). The term basically represents the sound or concept of a penile erection

Erection

Penile erection is a physiological phenomenon where the penis becomes enlarged and firm. Penile erection is the result of a complex interaction of psychological, neural, vascular and endocrine factors, and is usually, though not exclusively, associated with sexual arousal...

 rising.

The slang term schwing is a close English equivalent.