Haida is very submissive and shy around Retsuko. As a spotted hyena, this makes sense as spotted hyenas have matriarchal societies where the males are submissive to the females.
Ton's using an abacus was meant to reinforce how he is not good with technology. However, people skilled with abaci are known to be able to do faster calculations compared to those who work with calculators.
Retsuko telling Kabae she was relieved because she was able to poop again after not being able to a few days (a lie to cover up the actual reason) gets so twisted by the time it reaches Haida, he's freaking out because he thinks she's pregnant. It's especially jarring to Retsuko, who outright asks if she's even looked pregnant at all lately when questioning why he's panicking. While Haida's not totally aware of it - and nor are the viewers - his overreaction is one of the first signs of his crush on Retsuko and how badly he's already hoping Retsuko isn't taken.
The way Retsuko lands after jumping actually goes a ways to show her growth as a person. In the beginning, when we see her talk about her idealism with her job, she slips and sprains her heel after taking a leap. She's not really prepared for taking that first metaphorical leap into adulthood, and she will have to face the troubles of the world, and she stumbles and falls. As any young adult will do. But, at the end of the season, she takes the leap again but lands sure-footed on both her feet. She has experience and has worked past some of her troubles. She still has many of these troubles, and will have to face them, but she has learned how to better face and recover from them on her own. In other words, she has learned how to land on her own two feet, both literally and metaphorically.
Right after Gori and Washimi talk to Retsuko about love, Retsuko sees Resasuke on her usual train, though he's not paying attention... and an outline/shadow of Haida can be seen in the background. Haida himself discusses Loving a Shadow a few episodes later with regards to his feelings about Retsuko, and it makes sense at this phase that Retsuko knows little about Haida outside of work despite his crush on her.
Ton says he didn't remember a thing from the drinking night, but he goes right back to his old personality. If he really did forget everything that night, he would have continued looking for whoever ratted him out. He likely remembered everything and just decided to drop the subject. It could either be because he now knows that Retsuko has connections that go above him, or he did realize he was harming his employees with his brand of "management". When Retsuko started apologizing for "rudeness" he knew she would drop it if he did, and claimed to remember nothing.
Washimi warns Retsuko about the downsides of marriage during their chats in the first season. It wasn't just advice or concern. Washimi knows what she's talking about as she reveals in the second season that she was married before and divorced after only four months.
Retsuko and Shirota: Retsuko breaks off with Shirota and later learns Shirota finds someone else when she's interested in him again. But would any relationship together even last? Given her bad luck with Reasuke and Tadano, Shirota may have had a character flaw that would have lead to yet another breakup. Throw in Retsuko's mother meddling in their affairs and it could have gotten really disastrous.
Episode 10 has Retsuko's summation of what she's learned over the course of the series start over Haida's Anguished Declaration of Love, and ends with the jumping and landing on both feet. "Metal Christmas" shows there is still a bit of a problem, however, in her turning down Haida and dealing with the end of Resasuke's break-up. It's unclear where the summation would actually work as a result, considering more drama comes up surrounding Haida's over-enthusiastic proposal and Retsuko's obsession with dating and social media over the Metal Christmas special.