Height: 165cm
Weight: 57 kg
Chest: 89 cm
Blood type: A
Birthday: May 12
Zodiac Sign: Taurus
Specialty: Super High-school Level Nurse

Tsumiki is easily intimidated to the point of tears. She is a nervous girl who constantly worries over bothering people and stutters over words, even going as far to ask Hinata whether it would be alright to remember his name during her introduction. She is quick to conclude that she is disliked by those around her, and her fragile personality makes her an easy target for Hiyoko Saionji's cruelty. Tsumiki frequently offers to let herself be beaten up or to strip, showing that she'd do anything at all as long as people do not hate her. She is also clumsy and often somehow ends up in extremely embarrassing poses, all of which she apologizes repeatedly for.

Tsumiki ends up getting the despair fever after tending to Komaeda in Chapter 3, and gets her memories back. After that, she kills both Mioda and Hiyoko. During the third trial, Tsumiki's ability as a Super High School Level Nurse backfires when Komaeda reveals that Mioda was not killed by hanging herself, but rather by being strangled according to the marks left on the rope. This reveals that Tsumiki lied when she did Mioda's autopsy, as she told everyone that Mioda died by hanging.
It can be noted that during the first half of the third trial, Tsumiki's usual stutter has disappeared for the most part and her willingness to speak up has also increased. After she is suspected to be the culprit, her persona starts to crumble and her personality begins to hop between her usual shyness to a more hostile attitude or to a more sarcastic attitude. She tries multiple times to convince the jury that she is not the culprit, but her plan backfires when her points only lead to her digging her own grave. After she is voted guilty, she stops struggling and Komaeda reveals she succumbed to despair fever. Komaeda states that he will never be able to forgive her because she killed out of despair and not to escape the island, but Tsumiki argues that he is wrong and that she killed for the person she loves. In addition, she reveals that her despair fever brought her memories back, where she now remembers what happened during their time at Hope's Peak.

Tsumiki claims that while she was genuinely shy and deeply feared hatred from others during their time on the island, she was always filled with despair and had an inner hostile / sarcastic side of her in real life. It can be noted that she was also deeply in love with Enoshima Junko and would do anything for her because the latter accepted her.

In her final moment, Tsumiki claims that her friendship with everyone on the island is "just history," as they cannot remember their real personalities. Essentially, she is the first person to leave behind her hatred for the world and destroy her bonds with everyone before her execution.