Deceased parents, like battle mechs and nosebleeds, remain a common plot device in many anime series. Some parents die in spectacularly dramatic ways, like dying in blasts, being eaten alive, or even being murdered by their own children. Others pass in more everyday ways, like illness, car crashes, or childbirth.
Despite the frequency with which the trope appears, it serves as a catalyst for compelling character development on the part of their sad orphaned children, and can help darken the mood of a particular series. Vote up the characters whose loss affected you the most, and left you wishing you were watching something happier, like Digimon. Oh, wait, Iori's dad passes away in Digimon. Never mind.
His mother killed herself by jumping in front of a train because she was afraid of him.