Family & blood relatives who kill each other.

[Njr Scrawl]

Anime has many of these. Fathers, mothers, brothers, sisters, sons, daughters, cousins, nieces, uncles & aunts.

Which killers & victims have stuck in your mind most, shocked you most? PLEASE USE SPOILER TAGS

[Orihimes_Boyfriend]

Its a running theme in Claymore. Like with Zaki (Rakis' brother) killing there parents

[DiRF]

FLCL... sort of... except it turns out to be a robo-dad, not the actual dad.

[Orihimes_Boyfriend]

In Code Geass. I mean Lalouch has killed of a couple of his siblings by now.

[jcrharris]

Hokuto No Ken has many cases of fratricide (though not direct blood related in every case).

James

[joelgundam01]

Princess Resurrection - Hime's siblings are killing each other to get the thrown.

[Doom85]

-Itachi Uchiha from Naruto killed off his entire family/clan in one night save his little brother. Nothing too shocking about that considering the setting of the story, until (manga spoilers) you find out he was under order by some of the higher-ups in Konoha, and the alternative was letting another world war begin, so he chose the path of a "villain" and lied to his brother so that he could avenge his clan and become the hero of the clan. Cue manly tears from this poster.
-While he doesn't actually do it, IIRC Light of Death Note actually has considered the possibility that he might have had to kill his father at some point. I think he even considered his mother and sister might have to die too if necessary, but I think he ultimately decided he couldn't do that (probably the one moment where I felt Light showed a genuine humane side).
-Envy from the first Fullmetal Alchemist anime wants nothing more than to kill the father that abandoned him, and his children too if he can. He succeeds in the former, and does manage to kill Ed, but of course it doesn't stick.
-Lord Genome of Gurren Lagann probably can't count how many "daughters" he's killed

[Buckeye]

Strain - Sara kills Ralph in the climatic final battle.
Code Geass - Suzaku killed his father in a flashback scene.

Those are what stick out the most.