User blog comment:B214/Volume 21 info & spoilers/@comment-99.118.13.217-20160603030142/@comment-1359322-20160603033759

@anon, You do realize that there's no guarantee that the sealing will be successful through sacrifice.


 * 1) The Bible God sacrifice himself to seal Trihexa and what happened? Someone still managed to unseal him. So sealing 666 is meaningless because eventually someone else will still unseal him.
 * 2) Rizevim would take into account on the leaders trying to seal 666 again, so he may have used the Holy Grail to make Trihexa immune to sealing. So normal sealing may be useless.

Also do tell me in what way or what manner that killing Akeno show that it meant business?
 * 1) Is she some prominent figure to the world that killing her would shock the world, it would demoralized everyone fighting 666.
 * 2) Is she someone so powerful that killing her can show how dangerous 666 is, it would demoralized everyone fighting 666 because it can kill her?

If you really want some killing that shows that it meant business then it should be someone like Odin, Zeus, Sirzechs or Thor, people who are powerful and prominent to the world, not a teenage who's barely have any impact on the world.