Those who patronize their local Burger King next week might have black teeth by the time they leave.

Burger King Japan announced Wednesday that its popular “black burger” series will return on Sept. 19 and be blacker than ever.

This time, the fast-food chain will introduce two new burgers featuring black buns, black cheese made with bamboo charcoal, and an onion sauce mixed with squid ink.

The Kuro (black) Pearl, priced at ¥480, will have a 115-gram patty, black cheese and sauce sandwiched by black buns. The Kuro Diamond, priced at ¥690, is similar but comes with a dash of color in the form of lettuce, tomatoes and onions.

Originally launched on a seasonal basis in fall 2012, black burgers are part of the company’s effort to introduce unconventional burgers. It was its best-selling new product in 2012, Tokyo-based Burger King Japan said.

This year’s burgers will be blacker as the cheese will be black. The dark delights will be available until early November at most Burger Kings in Japan.