'Nezulla: The Rat Monster' aka Saikyôjû tanjô Nezura (2002) - Kanta Tagawa.

Nervy, thrill-seeking teens break into an abandoned military laboratory and are brutally attacked by a raging, preternaturally swift, deadly plague-bearing mutant rat! To stem the outbreak, an ill-equipped squad of soldiers soon find themselves locked down in the derelict facility, almost wholly at the mercy of, Nezulla, a genetically altered, freakishly enlarged, brutally soldier goring killer rodent! Kanta Tagawa's bestial Nezulla remains an entertaining, low-budget Japanese S.O.V creature feature that zestfully recollects 80s Sci-splatter-fests 'Creepozoids' & Roger Corman's 'The Terror Within'. I've always dug a gnarly creature feature, and 'Nezulla: The Rat Monster' does a credible job of ticking all the more boisterous B-Movie boxes. The performances are robust, the gung ho narrative even makes room for moments of genuine pathos, and the practical FX are pretty sweet!