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.
YMMV: Kenichi: The Mightiest Disciple
Arc Fatigue - Kenichi's development has gotten this reaction as of late with many claiming that his growth has stagnated ever since his rematch against Tirawit which occurred about 150 chapters prior to the most recent chapter.
Ass Pull - Shigure Kosaka's ultimate technique: Soutou Kyourenzan, which is telekinesis limited to weaponry. Even in a setting like this, such a technique is off the wall.
Broken Base: The fan-service. You either find it enjoyable to a certain degree, or it's an unnecessary distraction to those who are reading for the fights and storytelling. And it just gets much more blatant, and in-your-face, as the series goes on; further alienating the detractors. The worst of it being the manyweird- angleshots of a helpless Miu seen throughout the Amusement Park arc during what is supposed to be an intense fight between Ogata and Tanaka.
Cargo Ship - Kii Kagerou x Setsunamaru (his sword). Completely canon; when he is forced to use another, he apologizes aloud for cheating on her. He also frequently calls her "beloved". It's even reciprocated.
Siegfried's first love was a violin.
Complete Monster - YAMI master Silcardo Jenazad couldn't stand lasting peace, so he incited a civil war, which he's still actively maintaining, in his own country 20 years ago. During said ongoing civil war, one of Jenazad's servants informs him that the men, who joined his side, because they were devoted to his cause, will die in large numbers if they persist in the current segment of the conflict. Jenazad's response: "So?" For his research purposes Jenazad causes his past students to fight and kill each other. He causes an avalanche to kill his own modern-day YOMI student, who, granted, isn't a very nice guy himself to begin with(except he survives). Jenazad also almost manages to trick fellow YAMI member Akira Hongo into killing the titular protagonist as well as kidnaps and brainwashes Furinji Miu into becoming his newest cold-blooded disciple. He later supervises the brainwashed Miu's battle against Kenichi, with the expressed purpose of getting her to kill Kenichi, following which her mental state will be completely subject to Jenazad's manipulation and the brainwashing process to convert her into his thinking will be complete. Jenazad detests peace so much he is willing to kill his country's deposed princess (the sister of the aforementioned 'dead' YOMI disciple), who is all for restoring peace to the nation. Silcardo Jenazad winds up being the only Nine Fist member to get killed off for real - by a fellow Nine Fist, the aforementioned Akira Hongo, no less.
Crazy Awesome - All of the masters are crazy and awesome to various degrees. Siegfried, the guy who spins around like a top and sings while pounding his opponents into dust also deserves a mention.
Shigure gets a crowning moment of Crazy Awesome in chapter 285. She and Kenichi are ambushed by three skilled assassins after Shigure's head. She takes out all three of them (two of them with her hair ribbon) and left all three alive. Awesome enough. What puts this in Crazy Awesome territory is that she does all this while completely naked. Also randomly decides to terrify waitresses with shurikens and thrashes delinquents with spoons.
Over the course of their two battles, Akisame Kotetsuji and Alexander Gaidar attack one another with sculptures made from steel rebar, carve statues out of rubble and generally turn whatever place they're fighting in into an art museum.
Siegfried also counts.
Ensemble Darkhorse: Renka, despite not appearing very much till about chapter 310, is incredibly popular.
Maybe 1 in 8 to 10 title pages for each chapter, really.
Foe Yay: Some people claim this is the case between Sakaki and his Rival the God Fist. After seeing this page, they may be on to something. Although they were just kicking the two people behind the other.
Both of Renka's fights against Rachel. In the amusement park, they end up wrestling each other stark naked. Also, Rachel didn't strip them for attention, since there was no one there.
This is more of a Pair the Spares kinda thing due to it being blatently obvious that Kenichi is Miu-sexual.
Too Dumb to Live: Kenichi's refusal to fight women is depicted as chivalrous (especially by Miu) but in reality just gets him beat half to death by enraged female characters (e.g. Kisara) that he refuses to defend himself against. This is especially frustrating when coupled with Miu's god-like martial arts skills - every single time he is shown sparring against her or Renka, it always ends the exact same way.