Kiryu can put a decal of Haruka on his taxi. It leaves the impression that he has become a Doting Parent.
Alternatively, Kiryu's taxi can have an Itasha decal with an anime girl suspiciously looking like Hatsune Miku. Not only does Kiryu mention that his boss, Nakajima, would likely be unhappy about it, but you also get a trophy for buying it.
One of Kiryu's early substories is called "Cyberterrorism" in which the taxi stand gets hit with a computer virus flashing pop-ups over and over. Kiryu may be The Ace in a lot of things, but computer know-how is not his forte, especially since some choices involve smacking it. The real solution involves to first unplug the modem, but that makes some very...suggestive moans come from the speakers to "put it back in." They put it back in and Nakajima is ready to unplug the computer until Kiryu stops him. That's when Hirakawa comes in and fixes the problem and says the company needs to put in some antivirus software... and that this virus comes from porn sites. Cue Muramatsu and Nakajima playing dumb.
If you can get past it being That One Sidequest, where you lose it you fall once, Saejima's "Cold Ramen" side story. Saejima has to walk on ice to deliver a bowl of ramen to a customer, while several people have fallen and are helplessly sliding toward him. A lot of people failed it simply due to the hilarious and unexpected absurdity of it.
Saejima can learn the 'Essence of the Snow Man' Heat Action, where he throws a guy onto the floor, rolls him up in snow, to the point that he becomes a large snowball, and finally makes a snowman out of him. As the coup de grâce, he puts a carrot onto the snow man in the most badass manner.
Daijiro Saigo, Akiyama's trainer/military fetishist is back, and suspiciously has hair this time. Saigo gets upset when Akiyama asks why he stopped shaving his head. If you manage to knock off his toupee while fighting him, he stops everything he's doing to go put it back on.
Shinada, so much. He serves as the game's Plucky Comic Relief, and he's such a strong contrast to the seriousness seen in Kiryu and Saejima. The conversation before his boss fight with Teppei Ono is definitely unlike anything said by the others before him.
Completing Haruka's mentor missions reveals a rather uncomfortable truth about her costume. It was made for Uda, who once dated Yoko. Not only was Haruka wearing a costume designed for a guy the entire time, but that means Uda used to be an idol as well! The two meet again and reconcile to Haruka's confusion.
Haruka: ...I have no idea what's going on.
In the next-to-final chapter, like the others, Haruka can visit a certain master to raise her level cap, but unlike the others, she won't engage him in physical combat to do it. The solution? After Sosuke brings him up to speed on dance battles, old man Komaki decides to adjust his style so he can take Haruka on in one. Sosuke is clearly amused.
In Premium Adventure, Kiryu and Haruka can take photos together and add captions to the good ones. A golden example◊.
When the two visit the TV Tower in Keneicho, Haruka declines an offer to eat at a restaurant at the top of it, saying she needs more exercise anyway. Kiryu chuckles to himself, thinking that deep inside she's still a kid. Cue a frown on her face, as she knows exactly what he's thinking, although he quickly denies it.
New to the karaoke scenes is the interjecter dancing when they're doing well. Kiryu moves his arms like he's directing traffic, Saejima is punching the air and looking like he's charging his HEAT, and Akiyama does a fantastic little disco shimmy.
Some fans might be disappointed with Haruka's gameplay, since she dances as opposed to the fights expected of other protagonists. Granted, it wouldn't fix her image, but that hasn't stopped hackers from being creative. A simple switch of Kiryu's model with his adopted daughter can lead to this. Looks like Uncle Kaz has taught Haruka a thing or two.
One sidequest has Saejima trying to lure in a group of "Santa Hunters", leading to the sight of him dressed up as Santa Claus, complete with a beard. Of course, Saejima ends up getting pestered by a group of kids asking for presents. This then leads to a brief Chase Battle where he runs away from the kids with "Jingle Bells" playing in the background.
Two of Akiyama's substories has him participate in a Dance Off, one with a street punk, and another with a Cool Old Lady. Akiyama's reactions to getting roped into dance battles are full of Akiyama's usual snark.
Hide: A dance battle! If you win, you'll be known far and wide as "the man who beat Hide"! Akiyama: I think I can live without that title. Hide: But if you run, you'll forever be branded "the chicken who ran from Hide." You wanna live with that, yo? Akiyama: I keep telling you, I'm not a dancer. Hide: You sayin' you're cool with being a chicken? Akiyama:I didn't say that, yo.