In the Rockman X4 manga, the Reploid military of the Repliforce rebels against humanity for independence after being falsely suspected of involvement in a city's destruction and ordered to turn in their weapons, with Jet Stingray being one of the Repliforce sub-commanders leading the rebellion.
One of the Maverick Hunters, Zero, battles him at sea after he destroys a city, and manages to slice off Stingray's helmet. Stingray compliments him and says he likes fighting strong opponents and that the Repliforce Colonel taught him to be ready to step into danger at any moment.
(This is the specific page I'm referring to about with regards to usage of 一つ): https://www.facebook.com/justbeamegaman/photos/a.1082047715222991/1082050911889338
He says 一つ at the beginning of all of his remarks to Zero in this instance. I know it normally means "one" or "once" or "only", but from the context here it looks like he is randomly saying it as a motivation shout, a kiai, similar to how one can shout "Geronimo!" in English as a motivation phrase, or "Chesuto!" in Japanese.
Is it normal for 一つ to be shouted in this manner, and can it be randomly shouted to signal excitement or motivation?