Here in America, April 1 is April Fool’s Day. In Japan this year, it will be the day Kaz Hirai takes over as CEO of Sony, replacing Sir Howard Stringer, who will remain as chairman of the board. On some level, Hirai must wish it were just a joke. Sony has been reeling for years as it struggles to make its disparate electronics and media businesses add up to more than the sum of the parts. Hirai comes from the PlayStation division, which has been one of Sony’s comparative bright spots in the last few years, but even the PlayStation brand is looking a bit frayed these days. His first big task as CEO will be to make Sony’s $1.5 billion buyout of Sony Ericsson pay off by turning Sony into a mobile phone power. But he has a long road ahead of him to turn the rest of Sony around.