[LillyFields]

The character is a type of sanscrit called bonji (梵字), or more correctly, in the style of bonji. It symbolizes the Amida Buddha (Amitābha) who is associated with salvation of the dead.

Actually, the bonji character is a bit incomplete, which may indicate Oiwa's inability to "jobutsu suru;" ie, leave this earthly plane and move on.