I'm looking for any good shounen/seinen manga with protagonist that's calm or expressionless.
Hot-headed/passionate protagonist seem to be the norm in shounen mangas that they're a bit boring for me 😛 I much prefer cool-headed/indifferent/egoistic/anti-hero protagonists.

Something like Ryoma in Prince of Tennis (arrogant type and he's usually pretty calm), Kuroko in Kuroko No Basuke, or lazy/calm protagonist of One Punch man, Noblesse protagonist,or egoistic anti-hero characters..or the protagonist in Sword Art Online (anime), very calm.

Works I read/reading with calm/expressionless protagonist:
Dr. Frost
Noblesse
One Punch Man (I like his "lazy" trait too)
Prince of Tennis
Initial D
One Outs
Kuroko No basuke
Noblesse
Death Note (antihero)
Jiraishin (crime theme)
Kokou no Hito (loner/quiet/calm protagonist)

Genres I don't like - Ecchi, harem
I would much prefer a shounen/seinen manga with sports/combat/dark theme.

I also don't mind shoujo mangas like Ouran Koukou, Last Game, Beauty Pop, where the heroine are very calm/expressionless.

Any recommendation will be much appreciated.

How about a genre + category search? Shounen/seinen + "calm protagonist" - harem and ecchi.

As for recs:
Mushishi
Liar Game
Saiki Kusuo no Ψ Nan
Historie
Ajin
Ansatsu Kyoushitsu
Majin Tantei Nougami Neuro
Ping Pong
Fushigi na Shounen
Ubume no Natsu + associated sequels and side stories.
Kuroshitsuji
Akagi
Usogui
Gunka no Baltzar
Funouhan
Yamikin Ushijima-kun

Will add more as I remember; I've got a lot of others I just need to recall. This is my favourite type of protagonist, too.

I did the category/genre search with tags in the past but the selection is quite vast so I thought it'll be easier to get recommendations from people.

Thank you very much for the recommendations 🙂

Some more titles:

Pluto
Rappa (SASAKURA Kou)
Yamikagishi
Goth
Takatou Shounen no Jikenbo
13 Club
Lost+Brain
Naki no Ryuu
Aventurier - Shinyaku Arsène Lupin
Mononoke -- Though I really recommend the anime for this one; it's much better than the manga.
Blame!
Freesia
Dendrobates
Yugo -- Once again, you might have to turn to the anime; but in this case because the manga hasn't been scanlated.
Number Five
Sanctuary
Spiral - Suiri no Kizuna
Black Cat
Munakata Kyouju Denkikou + sequel
Killer Stall
Mahou Tsukai no Deshi ga Warau Toki.

Calm female protagonist in shoujo/josei:
Kisshou Tennyo
Ciel - The Last Autumn Story
Stone Cold
Chang Ge Xing

Black Haze
Life Howling
Shokugeki no Soma
Wind Braker
Rain
[url=http://www.mangaupdates.com/series.html?id=75341][/url]
Akumetsu
A Fairy Tale fo the Demon Lord

Thank you all for the recommendations 🙂