I'm looking for a character that attached emotionally to the other, to the point that if that person disappeared, the character would crumble apart.

The perfect example is Yoite & Miharu Nabari no Ou or Nezumi's attachment to Sion No. 6

The second one would be a character that protective to their siblings
Ex: Wada Popcorn Avatar, Raimei
Any kind of media is ok (light novel, manga, webtoon, etc)

for the 1st one, perhaps:
-pandora hearts


for the 2nd,
D Gray Man - komui is overprotective of lenalee
six half perhaps

The first one:
07-Ghost - Teito and Frau
Shirogane no Ou - maybe? the bodyguard and the king (I forgot their names...)
X/1999 - Kotori and Kamui & her brother

And I second Pandora Hearts - it has many intricate relationships

The second one:
Ao no Exorcist - twin brothers Rin and Yukio
Annarasumanara - Ai's sister is more of a side character, but I'd still suggest you read it for the amazingness of the webtoon
Angel Beats (anime) -

Well for the second one there's Fullmetal Alchemist

Thanks for the suggestion!

I've already read Fullmetal Alchemist, 07 Ghost, Pandora Hearts, X/1999, Annarasumanara, D Gray Man, and watch Angel Beats!. I'll try to read six half and Shirogane no Ou.

Moar please?

i second six half.
akatsuki no yona

dengeki daisy

kamisama hajimemashita (as you can see, i'm recommending mainly shojos what can i say? i love my good shojos )

kuroshitsuji

hana to akuma

Kare Kano. yukino may be the only person who keeps arima from falling part.

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"In a world where most people would be crazy, then it would be normal to be crazy and crazy to be normal... but then again, if you were normal, then you would be crazy... isn't it crazy what a paradox a little craziness can create?"

NG Life
He's really attached to all the people from his past life, and terrified if he can't remember anymore.
Really good character's. One of my favourite mangas!!

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~Be Bold, and Mighty Forces Will Come to Your Aid~

"I loved you
so I drew these tides of men into my hands,
and wrote my will across the sky in stars"
- T. E. Lawrence