Is there a reason she keeps saying "poi"?
Excellent question.
Kotaku's in-house nautical anime girl expert Toshi Nakamura,
who wrote about
Kancolle way back in 2013 (2013!), explains that her use of vague language is due the differences between the way many Japanese and Westerners view history.
Huh?
Okay. A little context. In
Kancolle, the characters are personifications of Japanese battleships (though, there are a few German ships). So Yuudachi is the Shiyatsuyu class destroyer, Yuudachi. In the
Japanese account of the ship's final battle, which is far more heroic, the ship went straight through the enemy fleet and flanked them, sinking two American vessels and disabling three more before being disabled. In the
Western account, the Yuudachi torpedoed one ship and then was seriously damaged by U.S. gunfire. It was a night battle, and perhaps there was confusion. It seems the character's creators have used this uncertainty to create the "poi" catchphrase.