Little nothing is known about Tanaka except that she knew Takashi and Rei while they were in elementry school and that she passed away at some point.
Tanaka's physical appearence is unknown.
When Takashi was young, he was playing tag with his friends in Tanaka's yard and accidently broke her fence. Despite this, she did not scold him because the fence was already damaged. After she died, her house was left abandoned due to desputes over who would inherit her house.
From what Takashi said, Tanaka had apparently a kind personality as she did not get mad at him or his friends when they broke her fence.