Any suggestions?

Thanks!

Hi, I never read Brother x Brother, so I really don't know how Kaname is, try giving some more details, so I can help you in any way I can! 😀
Vulnerable in what way? Like, his humor is vulnerable, sometimes good and sometimes evil?
Or defenseless? Like a petit hamster you just want to take care? (ok, Okane ga Nai reference, get out of here!!!)
Haha, sorry for my examples.

In MyAnimeList, some similiar mangas recommendations to Brother x Brother are:
Aniki Joutou
Ano Hi no Kimi wo Dakishimeta nara
Nanahikari
Sakura Gari
Honeys
Love Home
Kimi no Ondo
CUT

But I don't really know if there are vulnerable characters in these ones, sorry. If you give me more details, I can help.

Hi, thanks a lot for all the recs, gonna check them out! (:
What I meant by vulnerable is exposed to many possibilities of being harmed, easily upset, traumatized, that sort of thing.

Maybe

End Game
Aiso Tsukashi
Konbini-kun
Nichijousahan Bi - Beautiful Life
Nureru Karada (YAMAKAMI Riyu)

Thanks a lot, will definitely check them out.

I haven't yet read Brother X Brother yet either but I can think of a few manga with vulnerable characters.

Kanashii (Itoshii) Kotoba ( I love this one, the seme is a breath of fresh air)

Hinata and also Jouzetsuna Yubi both are one-shots from Naono Bohra, actually she probably has more that fit your theme than I'm recalling the titles to at the moment.

Doushitemo Furetakunai haven't read this one in while, but I think it fits.

If I remember any more, I'll edit this post.

Thank you, maladymaven!