Ui Tunesu (also known as Witness-chan) is a female student who attended Akademi High School in 1980s Mode. She was originally deleted because she was only made to show an example about how to get away with murder, along with Victim-chan. In "January Osana Progress Report Part 1", she was re-added just to react to Yandere-chan poisoning Osana's bento but then returned in 1980s Mode.
Ui Tunesu had red hair in twintails. Her eyes were red as well. She wore the Akademi High uniform with white knee-high socks.
Not much is known about Ui Tunesu's personality, but it is assumed that she had the Loner persona (formerly known as Coward), as that was the only persona for female students implemented at that time.