seppuku vs self-annihilation

seppuku and self-annihilation both are nouns.

Word	Noun	Adjective	Verb	Adverb
seppuku	Yes	No	No	No
self-annihilation	Yes	No	No	No

As nouns, self-annihilation is a hypernym of seppuku; that is, self-annihilation is a word with a broader meaning than seppuku:

seppuku: ritual suicide by self-disembowelment on a sword; practiced by samurai in the traditional Japanese society
self-annihilation: the act of killing yourself

Other hypernyms of seppuku include self-destruction, suicide.

seppuku (noun)	self-annihilation (noun)
ritual suicide by self-disembowelment on a sword; practiced by samurai in the traditional Japanese society	the act of killing yourself