These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The "Running Around The Streets" theme of River City Ransom, a major Ear Worm and very long tune by NES standards.
Almost the whole soundtrack of Kunio Tachi No Banka.
"Lover to Friend" as heard in the CD that came with one of the games.
Despite not technically being part of the canon, Target Renegade, an American sequel made specifically to the American version of Nekketsu Kouha Kunio Kun, earns a mention just because it's so cool.
CanonDiscontinuity: Target Renegade, which is a sequel to the American version of the first Kunio game, and as such released only in America. In addition, the Game Boy Advance edition of the Super Dodgeball series inexplicably dropped the Kunio cast, even in Japanese.
It's also been suggested that the Nekketsu Kouha and Downtown Nekketsu branches of the series may be Alternate Timelines, as it's never really explained how they connect, and some things are different in them; ie, Kunio and Riki having different girlfriends.
Ditto, the scene of River City Ransom with the sauna.
Sequelitis: It is said that Technos Japan's over-reliance on the Kunio-kun series, at the expense of their other franchises is what eventually drove the company out of business.
Uncanny Valley: A common gripe expressed by many fans about the two newest Kunio games released on the Nintendo DS. These games moved the series into the third dimension, and there's ample evidence they made an attempt to preserve the Super-Deformed, blocky proportions of their sprite counterparts, but a very unfortunate sacrifice was still made in the form of the facial expressions, which used to be surprisingly dynamic (and often funny) for such a distinct-looking series, and because limbs often cave into torsos and change size, distinct features are often obscured. To be fair, the games look a great deal better in motion, and the developers actually capitalized upon the 3-D engine by designing courses that utilize it creatively, but it still is a sad compromise.
Fortunately the Nintendo DS is approaching the end of its lifestyle, and its successor is much more powerful, so Kunio games in the future stand to look much better.