Any manga with a character who can't talk, or stutters or has some kind of speech impediment that plays a role in his lifestyle (his or her).
It can be romance or comedy just no horror or tragedy

There's no I in TEAM but there's a U in SUCK

Fruits Basket features a character who can't talk, but she's not a lead character. It's a very good manga.

TWGOK
Smash!

Mute Character Tag

"I'll shut your mouth~~~~~ with mine~~~"

二息歩行

Body Talk Paradox - if you're fine with yaoi, this is a favorite of mine. He stutters and has trouble expressing himself.

Bukiyou na Silent - another yaoi favorite. He also has trouble expressing himself, though it's a bit lighter feeling than Body Talk Paradox.

From Far Away - if this counts, the protagonist is the only one in the series who can't speak the others' language, so she has to learn it. As a result, her sentences are broken up and halting for a while til she gets fluent enough.

Full Moon wo Sagashite - pushing it, but she has a throat problem that doesn't let her sing, and I think she gets pains if she raises her voice or uses it too much.

Maybe Kingyo Sou. He's deaf, so he doesn't talk very often and uses sign language.

Helen ESP, this one has all of it "lost her sight, hearing, and ability to speak" and has a very charming Story.

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I think ookiku furikabutte fits somewhat. Though it is mainly about baseball, the main character is so shy and unconfident in himself that he always stutters and never can finish his sentences.

Only one of his teammates can actually understand his broken speech pattern.

I believe that the best mangas are still out there, waiting to be discovered.

Little Little

Akuma to love song a side character...
and Aoi Kiseki

maybe Jouzetsuna Yubi works? But it's a yaoi

Koyoi Oto Furu Sora no Shita

We work in the dark, we do what we can, we give what we have, out doubt is our passion and our passion is our task, the rest is the madness of art. Henry james

The World is Mine

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Quote from purple716

Is there any manga where the male lead has an illness known as stomach ulcers.Yaoi are fine top.