According to Production BaoBab, seiyuu Kawakami Tomoko
passed away on June 9th. She was 41 years old. She had been struggling against ovary cancer since 2008.
Director Ikuhara Kunihiko
posted on his twitter that he contacted Kawakami on March 14th. She told him that she wanted to play in his new anime Mawaru Penguindrum
Director Sato Junichi
said Kawakami recorded the drama CD of Aria
in September 2009. She recorded the voice alone because she was taking anti-cancer drugs and her doctor forbade her to be in crowds. The producers waited for five months until Kawakami's condition got stable. Sato said she was one of the irreplaceable seiyu.
Sources: Production Baobab
, Oricon News
, Ikuhara's tweet
, Sato's tweet