@cfatalis: I haven't finished the manga but so far it's nowhere near everyone dying... just read Dream's spoiler... geez that sounds crappy/loopy. Glad I dropped the series when I did.
I can't think of any where everyone does but a ton of people bite the dust in Saikano. Basically every named character with the exception of two people.
I'm not sure if this is 100% true but it is certainly implied
There is seemingly no 'perfect' way to truly say goodbye. So I gathered a bunch of them!