I don't care whether or not characters develop during a story, not as such. But stories cannot progress if there is nothing to write about! There needs to be something driving the story. That's fundamentally what a conflict is. Stories always progress towards the accomplishment of a goal, whether that goal is stated or unstated, and a conflict serves to create a goal, to underline an existing one, and to add a sense of urgency to the procedings. Stories without conflicts are stories without goals, and that means stories with bad conflicts don't progress towards anything. This makes them bad stories.

So Shizune is static. Okay, let's write around that. She's deaf, that's a source of potential conflict. Let's have Hisao genuinely struggle with sign language instead of being a complete natural, like he is here. Maybe he's bad at it. Maybe Shizune is dismissive of the fact he's bad at it, and mistakes his lack of aptitude for an unwillingness to really try hard. That's a potentially interesting character conflict, let's go with that. Maybe Hisao really doesn't want to learn for some reason, and he needs to come to terms with why. Maybe Misha is teaching him in this storyline and she's sabotaging him, consciously or unconsciously, and this needs to be discovered, aired out, and solved. Maybe the school just doesn't have good resources for learning sign language, as the existing story already hints at here and there. It'd be best to pull a little from categories A, B, and C together and weave them into one. None of these require Shizune to change or develop, because she's right: If he's genuinely trying, then he should be learning faster than he is. When the problem is resolved, he does, and he's able to really talk to Shizune for the first time. Okay, great! We've got Act 2.

Shizune is static. Okay, let's write around that. She gets on poorly with both her family. That's a source of potential conflict. And frankly, Shizune really isn't at fault for the situation; she's deaf, she can't help that, and her family isn't even trying to adjust or involve her. Okay, maybe some situation that comes up and escalates the low-level conflict there into a full-blown dramatic conflict. So when they go home, this problem needs to be solved. Akira is already on their side. Hideaki is convinced, and there's a sibling bonding moment. The three family members, combined with Misha and Hisao, start to mend the bridges between Shizune and Lilly; maybe the two of them develop some means of communicating that doesn't depend on other people, despite the nature of their impairments. Then they convince her father, and whatever the original family problem was that ignited Act 3 is solved. They're not there yet, but they're on the way to being a real family. Great, that's Act 3.

Now, we need an Act 4 topic. Because it's the final act, we need something that ties everything together. Ideally, it should be an "oooooooh" moment, where, when it's pointed out, you realize how this theme and this conflict has really tied the story together all this time. Shizune is deaf. How can we tie that into a theme? Well, looking at the Act 2 and 3 outlines above, you'll notice a common theme in both: Communication. Appropriate choice for a deaf-mute, I think. Shizune's a static character, and her big problem is communication. We'll strive to not develop or change her at all while still working in this theme. Now, how do we do this?

Hisao! He's our protagonist; let's have him do all of the character development. All of this time, he's been struggling to communicate with people, and he's gradually grown closer to Shizune and Misha. Now he's closer to Lilly, thanks to the events of Act 3. He starts hanging out with Lilly and Hanako now and then. Gradually, Hisao becomes torn; on one hand, he really likes Shizune. On the other hand, talking to Lilly and Hanako is fun, and due to some event involving them and maybe Akira and Hideaki, he's coming to understand that he actually really likes talking to other people. Not to accomplish anything, but socializing for the sake of socializing. He becomes involved with a larger and larger group of people. This is something that Shizune doesn't understand, and she's kind of domineering. This eventually causes a rift to form, because he isn't devoting all of his time and effort to Student Council business, not like she wants, and she doesn't understand what he's doing or why.

Hisao's task in our new Act 4, then, is to find a way to make Shizune understand his point of view. He loves her, and he doesn't want her to change; but at the same time, he's happier than he's ever been. How does he get this across to her, on top of his still-unspoken romantic feelings? The climax of the story now is getting Shizune to admit fault and apologize. For the first time in our new story outline, she was genuinely wrong, and thanks to Hisao's character development, she comes to respect his point of view, although she doesn't really understand it. Work a confession and sex scenes in here somewhere, ending CGs, roll credits.

Okay, my Act 4 outline is kind of awful as written, though the "Shizune is wrong for once, and is able to admit it" conclusion is punchy. Misha should be involved more in these Acts, too. And I'm honestly not a fan of Shizune not ever really being wrong otherwise, which a lack of development basically necessitates... But you get the idea. As presented, this outline is constantly driven by conflict after conflict, and all of them are unified under the banner of one greater conflict that in turn drives the entire story: Shizune has problems communicating with people. The entire story involves addressing this, bit by bit, and at the end, Shizune is communicating better with the people in her life and Hisao is in a place where he wants to and is able to assist her. And she hasn't really changed a whit.

(Look at Emi's route; it's an excellent example of this kind of overarching structure. Act 1 establishes the dramatis personae, Act 2 gets Hisao involved and makes him care, Act 3 introduces the central drama by means of many smaller conflicts, and Act 4 resolves it. I posted in more detail in that discussion thread, should be interested in details.)

Now, a lot of these elements are in the route as-is. But the story fundamentally lacks tension and drive and a strong sense of dramatic cohesion. Nothing drives the story, and as such it simply rolls slowly downhill, plodding towards a conclusion. It is, to put it in a word, boring. To put it in two and a conjunction, it is aimless and boring. That has nothing to do with character development and everything to do with conflict.