Let's start with Hirose. The only regular female cast, and she's essentially a dead weight. I actually thought she would have died in the first episode...no...it would have been better. Apart from the Hirose arc, what did she ever really do other than tell Kenzaki where the undeads are? And it's not like she got those information magically or anything. So I guess that's why in the movie she basically threw the undead searcher at Kenzaki; it's like, you can just do it yourself. Oh, she slaps his face in episode 2, I think, but that's about it. (I thought at first since she's kept, she might become a romantic interest. That thought died when Kenzaki started interacting with Hajime.) I guess I wasn't being honest last time when I thought I could even grow to like her, but since I hadn't finished then, I did try to keep an open mind. If I want to read into it, maybe she gets jealous that Kenzaki spends a day following a bratty teenager around.
Speaking of bratty kids, I thought Amane was cool at first, but now (probably the movie's influence) I think her obsession with Hajime is borderline dangerous. And why her mama says or does nothing about this? In fact, why let Hajime stay at all? When he left on his own, she should have felt relief, not worried. (What kind of mother let her kid walk around town by herself? Amane is also rude to her uncle when I don't see what Kotaro has done to have earned that kind of disrespect and her mother let her get away with it. This girl simply doesn't get enough discipline--or maybe she doesn't get any.)
Tachibana's girlfriend had potential, but I think she was wasted on bad/strange dialogue and not having enough chemistry with him. I really wanted her out of the show because she was useless in bringing Tachibana back from whatever personal hell he was in. While it did surprise me that Isaka killed her (I just didn't expect such a drastic measure--after all she didn't seem to be a real threat to Isaka; blame me for looking at things on the bright side), I accepted that it was necessary to destroy Isaka's influence on Gallen (since obviously nothing else works now).
And then there was a similar thing going on with Mutsuki and Nozomi. At least Nozomi was marginally more successful in pulling Mutsuki back (but then that might be only because Mutsuki was a weaker-willed character than Tachibana).
Just when I thought I had enough of Nozomi too (I might not actually want to strangle her, but I came close after hearing her shout 'Mutsuki' for the upteemth time), she disappeared like ten episodes and left Mutsuki suffering alone (yes, he wanted it that way, but the way everyone left him was more like so they could go do their own thing than them complying to his wishes). And my wish regarding Mutsuki didn't come true, after all. I was actually hoping if Spider possessed him, at least turned him into someone truly bad/evil, someone to be reckoned with, instead of the half-and-half I saw. As it was, I think he was just an annoying teenager with serious attitude problem. No wonder no one (not even Nozomi) devoted any time for him anymore; he wasn't really a threat. (Though I still maintain they left because other plotlines call them; I'm not sure what happened to Nozomi at the time, however.)
Yeah, it is regrettable that there is no human female I care about (as far as I'm concerned, that photographer who is suspicious of Hajime is better off staying in KR Agito). But at least I like the tiger undead (who, along with most of her race, seems to treat the undead form as a monster form and reverts back to human form after a fight, so, except for the green blood, I like to pretend that she's human). She and Shima-san are instrumental in bringing back the real Mutsuki--and no matter how unbearable he had been, I think it was still sad that the humans abandon him and it took two undeads to humanize Mutsuki again. And they both approved of Nozomi--which is when/how I know she won't suffer the fate of Tachibana's girlfriend. :(
Speaking of Tachibana, I sort of get fed up with how long he is going to keep doing the right thing for the wrong reasons--or more like the wrong thing for the right reasons? And what significant thing(s) did he do while being Hirose's lackey anyway? Trying to capture Kenzaki? Which he never did succeed (or did he? I'll definitely get all the details after a re-watch). It will be better (more productive) use of his time to go back to deal with Mutsuki.
I think the problem with Tachibana is they first showed him as this senior, experienced rider, but then made him have faulty judgments and trusting people he shouldn't have relied on. He seemed to have learned, for a time, and then became gullible again. This is a character who has betrayed the others twice (or trice--if I count that first time--which was more of him being secretive and not confiding his plan to others), yet they still welcome him back with open arms. I see a lot wrong with this picture. And yes, I remember Kotaro's speech about being betrayed a hundred times is better than doing the betraying once....but still, these people are simply too forgiving. No wonder Tachibana doesn't completely learn the error of his way. (To be fair, I think Tachibana was treated with suspicions at first, but I suppose Kenzaki might have unconsciously caused others to forgive Tachibana...)
By the way, for all the people being wary of Hajime, I don't think he had betrayed them. (Well, it's maybe because they don't trust him enough to begin with, but I mean he never backstabbed them the way Tachibana did; except for the very early episodes, Hajime mostly kept out of the way). But my bias for this character is probably showing anyway, so feel free to discount it and believe he would backstab his friends (even though I really can't see any evidence of that). Still, I cannot deny that humans who have the misfortune to interact with Hajime do come into some unfortunate experiences.
(By the way, Karasuma is not the main cast. He's the writers' lame plot device who pulls things out of his toybox at the writers' convenience. I was naive to think him victim of circumstances at first. Victim of bad writings, more like. Shima-san is a thousand times better...)
(And Tennouji--it's pretty obvious this guy wasn't planned from the beginning. I'm disappointed, really, considering who his actor is. (I heard about that long time ago, too, and I would rather not, so if by some miracle you still don't know, you won't find out who he is...at least, from me.) I can sometimes like villain-like characters, but it seemed almost like the writers didn't quite know what to do with Tennouji and wasted most of the episodes he was in.)
Moving on to the titled character. He is not very easy for me to pin down, despite the simplicity of his character--probably because I don't have a grievance with him like I do with most other characters, but let's give it a try anyway.
Kenzaki is probably the most stupid hero or the most noble one. I like to go with the latter, even though I have to admit that he doesn't always make the best choices... (No actually, in his heart, he probably thinks he is making all the right decisions--but practically, the beginning of the movie scene is the ultimate right decision.)
I find Kenzaki has the most cheesy dialogue among the four riders. Or maybe it's just the way he says those lines--those standard hero thing like, I am a kamen rider, I'll protect everyone. I guess the lines feel cheesy because I actually believe him, believe in what he says, believe that he will carry them through, or dies trying. He has a sincerity which I never quite sense from the other three riders. (I'll cut Hajime (since he's not human) and (much as I dislike him) Mutsuki (since he's a confused kid) some slack, but Tachibana really has no excuse.)
So I always feel it unfair that other characters mostly push Kenzaki around (they either use him or oppose him at every turn). What kind of message does that send to kids? That being a nice guy doesn't pay? (I mean this more in a figurative sense, but with BOARD salary not in sight for Kenzaki, I suppose that could also be taken literally.) That being a villain is cool and fashionable? (Man, Amane probably believes that, though, what with her hating not!Hajime and all. Come to think of it, not!Hajime seems almost scarily like Kenzaki...and much as I like Kenzaki, I really don't need two of him.) But despite all that, Kenzaki still remains optimistic and see good in other people (e.g. Hajime), so I admire him for standing for what he believes in and for not letting the bad experiences jade his mostly positive outlook of the world. Standing up again and again and still trusting after being betrayed takes some strength (the strength which not every character--in fact, I'll say almost none of the character in this series possesses; oh sure, the others can be strong, sometimes, but they are just not consistent). Willing to fight for what he believes in, I think, is what makes him a real hero.
Yet Kenzaki is the least developed character out of the four riders. I like to think that was planned, though. He is the person whom the other characters come back to time and again after being mislead onto wrong paths. And he will not say one word of blame to make the others feel bad and simply accepts them back without being wary. It's like, they can be bad during the course of their journey, but they can always return (literally and as well as figuratively) to Kenzaki and be good again. (It's not even like he has lent them his strength or anything...in fact I did mention that they don't seem to treat him with respect all that much...but I think he's one of those pure-hearted types that make people ashamed to be bad, almost, so they just took out their bad manners at him to cover the embarrassment--take that bratty teenager who led him around, for example.) So it's utterly ironic that Kenzaki won't be around for other characters to rely on at the end of the series.
I don't really have a point to all this, except that I better stop here before I make this post even more confusing.
ETA: So it seems most of the points I've made about other characters had already been made elsewhere, and made better, I should say. I want to cry now. But at least my opinions on Kenzaki might not be copies, after all, since most I find on him is that he has the personality of a cardboard...