I have no idea how much Anno took from the manga since I haven't read it, but from sources it seems as if he chose to retain the elements of the plot and dialogue completely. In that case then it has to be Masami Tsuda's writing ability to be able to provide Anno with so much psychological insight to work with. Never since Kokoro Connect have I seen characters so brimming with psychology as those in Kare Kano. Toradora only reveals its cards fully at the last emotional arc. Kare Kano goes in all the way, with characters frequently ruminating on the exact scope of their relationships, worrying and analysing different aspects of their life from the very first episode.
Indeed Kare Kano is a wholly psychological romance comedy. It posits a method, that this is how people build personas of themselves, this is how group dynamics function, this is how personas are broken, this is how relationships are made. Anno's editing only serves to really emphasize the characterization a thousandfold. Episode 3 is a powerhouse of tempo, almost perfectly blending in the character reveals, the comedy, the confessions and the emotions to a fever pitch of an ending outpour. Drawing from his Evangelion experience, Anno uses deep reds, shadows, silhouettes and voids to accentuate Arima's psychological torment. When he recounts the slap his father gives him you can almost feel the weight of the palm.
Something tells me that most of the innovation is derived from budget. KareKano is sort of the precursor to Shaft's erratic style of editing, down to the text across the screen and the sound collage. Yet it is also completely minimalistic. Anno draws back on the art when the moment is not an atmospheric one but he always sees the need to draw very detailed aspect-aspect shots to establish a location. He uses manga art half of the time rather than animate the characters directly but the very nature of his editing makes it okay. In episode 6 (another atmospheric powerhouse) there is a moment derived entirely from manga shots scrolling rightwards. It works because the tempo syncs with the piano soundtrack and perfects the pace of a slow uncovering of memories. If majority of the romcoms out there had the editing capability Anno had, they would not only save on budget but would also be a whole lot more immersive.
If you think about it, by eschewing the background altogether for most scenes, or by stripping down the art, there's a greater motivation to express character's purely through psychological landscapes. Kokoro Connect and Toradora bask in the glory of having enough of a budget to draw out all the backgrounds and settings for their characters. Of course not everyone can be like Shinkai and maximize on their Romantic design, but rarely does a director think of stripping back the design until Shaft arrived in the picture.
Episode 6 does a kind of dual-ling thing where scenes are repeated but showing the two main characters different viewpoints. Moffat, when he made the television series Coupling, did the same thing in an episode used a split screen to show the aftermath of a breakup. Yet Coupling's main goal, being a comedy, was still the comedic payoff of having dual-misunderstandings and dual-synchronizations of two characters leading disparate lives. In this case though its used in the old Anno-esque fashion, of showing the clash between the misunderstandings of two lives, and the gaps between two hearts trying to get together. While Miyazawa was ruminating on Arima's great personality, Arima was feeling inadequate at Miyazawa's bright nature and questioning the veracity of his own life. As the episode passes and goes through a really melancholic atmosphere of rain and pent-up longing, it eventually culminates in this dual weaving with the method which I outlined above, using the right scrolling manga panels to indicate the joining together of two lives. (For those more interested in getting to know how Anno's camera works, a shot-breakdown of this episode is on the blog)
Episode 8's Act 0.5 is another very beautiful vignette, taking place before Arima and Miyazawa got together, dealing with Arima's slow realization of the emptiness of his own life and the development of his love. The whole atmosphere is a cooling down of the comedy-drama pacing that normally occurs. Great shots are developed, with cherry blossoms, haunting monochromes and red dusks. The manga drawing interjections here serve the purpose of ramping up the romantic feel, of having very clear and clean shoujo designs as opposed to the rawer animation, during the moments when Arima idealizes Miyazawa. The dusk scene when the two talk to one another is done with matching shots, and the correct framing to emphasize which parts of the conversation the characters are more invested in (a closeup of Miyazawa's eyes when she inquires about Arima not going to a private school despite having the funds).
With all that being said, the main problem is also its main strength, mainly the psychology. Being a romance manga, even with an astounding amount of character insight, and even with Anno's ability to draw moods, there is still the existence of genre conventions. As a result there is the episode with the school trying to interfere between the budding romance of the two, there is the episode with the love rivals and jealous alpha bitches that try to alienate Miyazawa from the rest of the class. Coming from the rich Freudian landscape of Evangelion, coming from the tight characterization of Toradora, Kokoro Connect and the cynical sociology of Yahari Ore No Seishun, it always feels that there's a huge amount of wasted potential. Especially with the knowledge that Anno later drops from the project (since I'm only at episode 11) makes it all the more depressing. Already though KareKano goes a farther way than most of the conventional plots out there by its willingness to delve into introspection rather than falling into the same old genre circles(I'm looking at you Shinbo and Nisekoi).
Whatever it is, KareKano is proof that even with the most rigid and overused genre, there is still loads of room to improve and loads of area to explore. It is a documentation of a skilled director plying his trade with a work that is not exactly in his realm of comfort. There's so much information to glean just from even one or two episodes about pacing and creating moods that its a wonder this work did not become more influential. Staleness is one of the great sins of any creator and if a work from about 10 years ago can outshine most of the works now then there's really a problem.
