Skymark airlines is an airline established in 1996 and it is the third largest airline in Japan by number of passenger. It was planned to operate a regular international route in the past but used to operate charter flights to Saipan. Therefore regular flights are currently operating only domestic flights.
Their hub airports are Kobe and Tokyo/Haneda. Skymark airlines is the largest airline using Kobe airport due to major airlines, JAL and ANA are mostly using Osaka(Itami) and Kansai(KIX).
Skymark airlines was established as a low cost carrier but actually it is not. They do not charge extra fees for baggage or seating as other LCC do. The differences from JAL/ANA is that there is no mileage program and mobile boarding card is not available. You must pick up your boarding card at one of the kiosks or at the check in counter.
Anyway, the airfares are cheaper than JAL/ANA and if you are traveling as a businessman, Skymark airlines is a good choice to traveling around Japan.