tourist visa extention

i have a 3 months tourist visa which is soon to be over.
i would like to extend it but i hear it's almost impossible and takes along time.
what can i do?
i got a suggestion to leave japan for few days (to korea for example) few days before the visa is expired and then re-enter ?
would i be given another tourist visa upon this second entry although it was only few days after the previous visa expired?

People from certain countries can apply for a 90 day extension inside Japan. Otherwise, quickly leaving and returning to Japan might be the best option, although, immigration officials might suspect you of doing illegal work in Japan.