Jiro Maeda wrote:

Minna,
A few days ago (September 2 in fact) I turned twenty, during that day,
thoughts ran through my head, thoughts that prompted me to write this fic.
I write this fic to answer the questions that popped in my mind that day.
By the way, although there are numerous (read: mountainloads) of fanfics
with Ranma characters in them there is no possible way of stopping people
like me from writing then , it's my favorite series, live with it!

Standard disclaimers apply

Rumiko Takahashi's Ranma Nibunnoichi

Growing up

"He barely touched his food Oneechan."  Kasumi looked up from the 

Shifts in perspective should get a new paragraph.  You don't want us
thinking that Kasumi just delivered that line.  

dishes

she was washing and stared into her little sister's worried face, oh

Comma splice.  "face" is the end of the first sentence.

 she

may deny it every time she could but the truth was that she did care for
her inaazuke.  "Maybe he's just not in the mood for teriyaki, Akane-Chan,
no need to get worried."  Akane bristled at this and the worry etched

Start a new paragraph with "Akane".  Start a new paragraph every time
you switch speakers.

 on

her visage was wiped clean.  "Who said anything about worrying for that
Bakatare hentai, maybe he was so full from eating a lot of Okonomiyaki

Decapitalise "Bakatare".  Comma splice.  Put a question mark after 
"hentai" and start a new sentence.

 and

ramen.  I think I'll go over to him and give him a piece of my mind." she
said, her voice getting louder every syllable.  Kasumi just sighed,
whatever state the relationship of Ranma and her sister is right now, she
knew that they had a long way to go.

"That sukebe, I should have known better than to be concerned with his
eating habits, it figures that he stopped over Ucchans and the Nekohanten
before going home.  He doesn't even realize that he's making other people
worry, that clueless insensitive......BAKA!  I'm going to go over the dojo
and introduce his face to the pavement, that's the least he deserves for
making me worry." Akane thought as she  headed towards the dojo, her battle
aura shining brighter than a new born supernova.  When she did enter the
dojo, the sight within had somewhat dissipated her rage.

OK.  So Akane hasn't grown up at all.  

Ranma was in the middle of the dojo doing a slow moving beginner's kata,

I rather doubt that Musabetsu has kata, but there's always that one 
anime opening to give a precedent.  

his every move spoke of grace and latent strength, his movement flawlessly
shifting from one form  to the next. His eyes closed as if in an inner
meditation.  Without warning, he stopped in mid stance and opened his eyes.
 "What do you want Akane?" he asked without even looking at her direction
as he toweled off.  Akane answered "I was wondering why you didn't eat much
today Ranma, is something bothering you?"  Ranma faced her and sat down,
motioning her to sit directly in front of him. "Akane, do you know what
today is?" he asked. Akane shook her head in reply, he smiled and
continued, "It's my birthday, I'm turning seventeen today." Akane felt
shamed, here she was berating him mentally for being insensitive and

Comma splice.  "Akane felt shamed.  Here she was..."

uncaring, when she didn't even know. Ranma saw the by-play of emotions on
his fianc�e's he tried to placate her with an answer, "It's okay, how

This sentence needs a rewrite.  "When Ranma saw the byplay on Akane's 
face, he tried to soothe her by saying,..." 

 could

you know when I never told you?" His efforts were rewarded with a smile,
"But that still doesn't justify why you didn't eat much at dinner." she
retorted, looking at Ranma seriously. He gulped at her scrutinous

Scrutinous?  Sounds obscene.

 glare and

nervously laughed "Well...  I couldn't focus on my food, I was thinking of
something..." he paused and stared at the dojo exit "I used to think that
when you get older, you get wiser.  Now though, I'm older by a year but I
don't feel different from what I was before. It seems complicated but..."
Ranma was interrupted by a laughing Akane, he frowned and asked what she
thought was funny. Akane replied "You should listen to yourself, I didn't
know your thoughts run that deep, but if it's any consolation, I think you
have matured Ranma, you've improved in your skill, you have gained a high
sense of honor, seeing as who your father is, that comes as a surprise.

This run-on sentence should be broken into it's components.  
"You should listen to yourself.  I didn't your thoughts ran so deep,
but if it makes you feel better, I think you have matured.  You've 
improved your skill.  You've gained a high sense of honour.  Seeing
who your father is, that comes as a surprise.  You've grown up Ranma.
Maybe not as much as you'd like, but grown up all the same."

You've grown up Ranma, maybe not as grown up as you'd like but grown up all
the same.  Well, I'm turning in now, Good night Ranma, happy

Period after "now".

 birthday."

With that Akane kissed him on the cheek  then stood up and left leaving a
confused Ranma absently rubbing his cheek.

end of story

Author's Rant: You might think that Ranma thinks too much, I say you never
see him think before, most people think of Ranma as a dumb jock, I on the
other hand think that there never was actually a situation where he is
forced to think.

Maybe, but my problem with Ranma in this fic is not that he's thinking,
but how he's articulating his thoughts.  Communication is a skill.  
One Ranma's never really mastered.  If he's opening up, he should 
stumble more, and he should express his thoughts in a distinctive 
character voice rather than the rather generic tone you have here. 
 
Something like, "I'm another year older, but it don't really make a 
difference.  I'm still the same jerk, doin' and sayin' the same stupid 
junk.  I should of figured that getting older don't make you smarter 
just by watching Pop," would give me more of a sensation that this 
really is Ranma talking rather than an authorial mouthpiece.

And no, I don't think Ranma's learned much about honour over the 
intervening timeframe.  But he has learned compassion which is a great 
deal better than his father did.