Koji Akiyama apparently introduced a new item to help batters with their swing during practice earlier today. From what I can gather from a Sanspo article, it's a support belt made out of stretchy material that gets wrapped around the lower waist to provide support. The idea is to wear this belt during BP for more stability.
Hitoshi Tamura told reporters that the belt kept his hip closed and that he felt more stability while swinging the bat. And Nobuhiro Matsuda said that it made him more aware of his lower body.