Zenko

Zenko (ゼンコ, Zenko) is the younger sister of Metal Bat.

Appearance
Zenko is a young girl with similar facial features to her older brother, with light skin and shiny black hair in a Showa era hair style kept around chin-length and clips aside with a clip. Her clothing is a light-colored cardigan & frock, high socks with frills and black Mary Jane shoes.

Personality
Zenko is just as strong-willed and headstrong as her brother but dislikes violence. She is caring and very protective of her brother. In addition, she is quite fearless as she was willing to go into an evacuated city during a monster crisis and was not afraid to stand up to Garou. Like her brother, she is very hot-headed, to the point of even arguing with Garou despite risking both her and her brother's lives. However, she is also quite humble, refusing to boast about her hero brother in front of other school kids.

Alien Conquerors Arc
Zenko has a piano recital during the alien invasion. She later calls Metal Bat, when he is arguing with Sweet Mask. She also asks for Sweet Mask's autograph.

Hero Hunt Arc
She calls her brother to ask for help with carrying her shopping bags, but Metal Bat tells her to wait because he is on an important assignment. This causes her to cry and hang up.

Monster Raid Arc
When Metal Bat is about to hit Garou, she shouts, "Big Brother!". Noticing that his sister is here, he stops his swing centimeters away from Garou's face. Garou takes this opportunity to punch Metal Bat and before the two could clash again, she risks her life for her brother and jumps right in front of Metal Bat and covers him in a protective stance and tells Garou about Metal Bat's promise to her. Garou listens, respects her wishes and accepts her persistence for anti-violence. He then quickly makes up an excuse and leaves the siblings alone.

After a brief conversation with her brother about how she knew where Metal Bat was, Metal Bat tries to go back to fighting Elder Centipede. Frustrated that she is unable to convince him otherwise, Zenko smacks him on the back of his head, unintentionally knocking him unconscious. She then tries to drag her brother home.

Super Fight Arc
She is later seen watching over Metal Bat as he is taken to the hospital.

Monster Association Arc
Zenko visits her brother in the hospital and watches the news about the Monster Association.

Abilities and Powers
Despite being a seemingly average human girl, she possesses a few skills that no normal girl at her age would have.

Physical Abilities
Enhanced Strength: Zenko can easily hold a flower bouquet that is almost as big as her brother with one arm. She was also able to (accidentally) knock Metal Bat out when he was injured.

Enhanced Speed and Reflexes: Zenko is surprisingly fast, as she was able to intervene between Garou and Metal Bat before they were able to clash again.

Enhanced Leap: She is capable of jumping fairly high for a child, as shown when she jumped to reach her brother's head in order to hit him.

Miscellaneous Abilities
Expert Pianist: According to her older brother Bad, Zenko plays the piano. She also appears to be quite skilled at it, as she got 3rd place in a piano concert, she participated in.

Trivia

 * "Zenko" (ゼンコ, Zenko) means expressive, diplomatic, and refined in nature. Zenko demonstrates these traits when she tries to negotiate a resolution with Garou.
 * In the 2017 One Punch Man Halloween cover, Zenko was depicted as a Japanese one-horned Oni. Zenko eating a yellow onigiri is a reference to the word Oni in onigiri.