When did Yukino and Yui fall in love with Hachiman?
It feels like Yukino started falling for him, once she realized that her personality and demeanor didn't affect Hikigaya in the way it usually does with normal people.
In fact, he couldn't care less about how she is, due to the fact that he was forced to join the club to begin with.
Yeah, he was a pessimistic bum who was antisocial, but that time being in that state allowed him to see the hidden nature and flaws of people, along with their tendencies.
This common ground between Hikigaya and Yukino, seeing the bad and ugly in others, and being subject TO that same bad and ugly, formed the basis of their relationship.
Hikigaya was different. Hikigaya was unique. So was Yukino.
They both saw things from the lowest of the low, and when they both realized that they have synergy with how they convey things, the seeds started planting themselves in all the right spots. This was widely apparent throughout the entire series.
Over time, they became comfortable around each other, being able to communicate and mingle in the only way they know how. They didn't receive the same flack they usually receive when they conversed among each other, compared to talking to normal people.
Although, on the surface, their conversations were usually filled with petty banter and the like, people like Yukino and Hikigaya are used to decoding the hidden meanings behind words.
Yukino isn't very good at conveying her feelings, or anything that's on her mind for that matter, which only leaves a few events in the anime that hint at her fondness for Hikigaya.
Their first &quot;outing&quot; in the mall. She was insecure as all hell.
Her displeasure with Hikigaya's solutions to club jobs. She reprimanded him for always throwing himself under the bus.
Her realization that Hikigaya contributes a lot to the club, often relying on him to find a solution to an seemingly unsolvable problem.
Her standing up to Tobe when he publicly talked down to Hikigaya.
Her reluctance to let Hikigaya use his way to solve the presidential election. She didn't want him to be self-destructive again.
Her voluntary discharge of his club membership. She wanted to honor his wishes echoed from when he got into the club in the first place.
The time in the nurse's office when they locked eyes for the first time.
When she kept the photo of them on that water ride next to her bedside pillow.
When she knew Hikigaya would come in and save the prom from being cancelled.
It's very subtle, and coupling Yukino's often reticent demeanor with that subtleness, leaves little to go off of other than what's made obvious.
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Yui is easier to discern. The initial spark was at the very beginning, when she witnessed Hikigaya saving her dog.
Ever since that happened, she's attempted to repay him back for the deed. Once she realized why Hikigaya told her to stop with the act, to free her from feeling indebted to him, she found out that Hikigaya isn't all about doom and gloom.
Another dimension to a seemingly dimensionless character.
She started seeing the other sides of him, and how, despite his outlook on life, he carries on with his solutions, paved the way for Yui to find her own strength to find her own path.
To take control for once, rather than be controlled. To actually feel like she did something for once, without following the flow of others.
Yui didn't think too highly of herself to begin with, that's why she started looking at him. Hikigaya was her role model. She looked up to him. That's why she started liking Hikigaya, for giving her the key she needed to discover herself.
She found herself getting swept away by his resolve to continue onward, quickly becoming entranced by his waltz.