Someone’s got to take responsibility. And that’s Toshiba Chairman Shigenori Shiga, who’s stepping down after the company’s multibillion-dollar loss was made public. Toshiba wants another month to prepare a report that will detail the extent of its writedown — estimated at $6.28 billion — and how it plans to move forward. The firm has been struggling after a nuclear deal by a U.S. subsidiary went wrong, and shares have fallen 50 percent since December. They fell another 8 percent today, and some analysts are wondering if the company has a future.