In her younger days she looked after Hayato and Yukino when their parents were out on business related meetings or trips. Their families would also vacation together and have been to an amusement park and zoo where she Haruno mess with them resulting in a fear of intense rides for Yukino.
She graduated from Sobu High School. According to Shizuka, Haruno wasn't the scholarly type, she achieved excellent grades without much effort. However, she was noisy during classes, didn't wear her uniform properly and was always participating in festivals. She was the chairperson of the cultural festival planing committee. She forced Shizuka to play the bass for the cultural festival volunteer band. Haruno made the Cultural Festival the most successful it had ever been.
It was mentioned by Meguri that Haruno took science as her career path in her third year. Haruno is currently studying for Bachelor of Sciences degree at a local Chiba university.
Haruno meets Hachiman and Yukino while they are out shopping for Yui's birthday. after some teasing she invites Hachiman out for coffee.
Hayato mentions Haruno can handle bullying better than Yukino. Haruno can use her facade to deflect andinfluence while Yukino refuses to lie/change to herself.
After the Chiba Mura Park trip, Haruno is waiting in the Yukinoshita limo to take Yukino home for the summer. Hachiman and Yui realize it's the same limo that hit him on the first day of school. Haruno greets Shizuka and meets Yui for the first time. She then teases Yukino and Hachiman before escorting Yukino away.
Hachiman learns about Haruno from Shizuka during their ramen date.
Later on during the fireworks festival Hachiman and Yui meet Haruno who invites them into the VIP viewing area. She explains she is there as her fathers representative, but it was her mother that decided that a long time ago. She also lets on that Yukino is generally kept away from public events to not confuse their "succession rights".
After the fireworks show Haruno offers Hachiman and Yui a ride home. When they are hesitant, Haruno explains the vehicle and Yukino was in an accident, but it wasnt Yukino's fault. Hachiman and Yui decline her offer and Haruno drives off.
Meguri Shiromeguri calls Haruno to help organize the Cultural Festival. Haruno manipulates Minami into letting her perform with her orchestra.
Haruno begins to influence the committee negatively and less and less people begin to show up.
Haruno begins to help Yukino out causing Yukino to work harder and longer than before. Haruno ropes Hayato into helping with the committee as well. When Yukino falls ill from overwork Hayato calls Haruno to let her know.
Haruno finds Hachiman's Festival slogan hilarious.
Hachiman begins to think Haruno shouldn't have this much free time to volunteer. He realizes Haruno is volunteering and being annoying to make Yukino come out of her shy shell and perform to the best of her ability.
During the Cultural Festival Haruno and her orchestra put on an entrancing performance.
Later when Minami goes missing Haruno delights in being able to either help or not help Yukino stall for time. She agrees to help Yukino when she realizes how much Yukino has grown. Together Yukino, Haruno, Meguri, Shizuka, and Yui get on stage to perform one last song while Hachiman looks for Minami.
After the festival Haruno calls Hachiman an awesome hero, and states his skills might be wasted on Yukino. She then compliments Yukino on an awesome performance and festival result.
Haruno email's the service club asking why Yukino has been so cold to her after the Cultural Festival.
The Service Club briefly considers asking Haruno for help with the Athletic Festival.
Volume 6.5 Bonus Track Edit
Yukino reveals Haruno ruined Santa for her when she was a child.
Hachiman accidentally finds Haruno in a cafe. She teases him and they talk about Yukino and the Service Club until they are interrupted by Kaori and Chika. Haruno manages to pry some stories about Hachiman's past out of Kaori. In return she agrees to call Hayato over so they can meet him. After Kaori and Chika leave, Haruno runs off to meet some friends leaving Hachiman and Hayato alone.
Later that night Haruno calls Komachi's phone to talk to Hachiman. She threatens him to make sure he will go on the double date with Hayato. She even mentions she knows where he lives.
Before the double date Hachiman runs into Haruno again and she mentions she will be spying on them. Hachiman catches glimpses of her here and there. Haruno only reveals herself after Yukino & Yui show up and Kaori & Chika leave. She says she is just there to try and motivate Yukino into becoming student council president. She tells Hachiman sometimes actions don't have any hidden meanings.
Hachiman and Yui meet Haruno who is with Hayato while out shopping for Yukino's birthday present. Haruno calls Yukino out to meet them. In the meantime Haruno explains she and Hayato are out with their family doing business calls for the Christmas holidays. When Yukino arrives they talk about various things until Mrs. Yukinoshita appears. The Yukinoshita's and Hayato leave to go eat dinner.
During preparations for the Pre-Valentines day event Isshiki called Haruno out to lend a hand. Yukino and Hachiman ask Haruno if she knows what Hayato's 3rd year school path is. Haruno coolly dodges the question and then asks Yukino what her own path is. Yukino does not answer. Haruno notices things are a little tense between Yukino and Hayama. She understands there is a rumour they are dating and mentioned this happened once before.
Afterwards Haruno made Hachiman walk her to the train station. Haruno starts to counsel Hachiman on what his future career should be. She advises him on Social Sciences.
A few days later Hachiman is meeting Haruno at a cafe. They discuss what Yukino's career path is. Haruno mentions Yukino doesn't trust Hachiman, but instead does something much more horrible (dependency).
Isshiki invited Haruno to the Pre Valentines day event. She felt that Haruno would be a nicer counterpart to Yukino despite Yukino being able to make delicious chocolates. Haruno mostly talked with Meguri and Shizuka during the event.
Eventually Haruno got bored and began to cause trouble. She told everyone that Yukino gave Hayato chocolate once. She then bugged Yukino about who she would give chocolate to this year. Haruno also tells the Service Club members that she thinks they aren't searching for anything genuine anymore. Afterwards she leaves.
At some point Haruno told Mrs Yukinoshita about Yukino's career plan.
Mrs. Yukinoshita makes Haruno go and live with Yukino to keep an eye on her. Haruno confronts Yukino telling Yukino that she needs to discover her "self", and stop following in Haruno's footsteps.
When Yukino stays at Yui's house Haruno talks to Hachiman on the phone stating he is "too kind" for always looking after Yukino.