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Ancient over-technology weapons always end up going out of control.
Literal
Ancient [genitive-の] over-technology [genitive-の] weapons [topic-は] without-fail control [subject-が] becomes-impossible.
Fantasy/SF trope vocabulary. オーバーテクノロジー is a Japanese-coined English-style compound ('over-technology') meaning technology so advanced it surpasses current understanding — a staple of anime and sci-fi. Native English rarely forms 'over-' compounds this way; it's actually a 和製英語 (wasei-eigo, Japanese-made English). 必ず ('without fail,' 'certainly,' 'always') pairs with a predicate that follows as an unfailing rule. 制御ができなくなる ('become unable to control') uses the construction [ability] + ができなくなる, marking a transition into the loss of an ability or possibility.