Fu/Ono
It’s Ono not Ôno/Oono/Ouno/Ohno!
Nelson’s #2382
斧 Fu・Ono ‘axe, hatchet’
斧鉞 Fuetsu ‘axe; battle-axe, curtailment’
As for which Ryûha in the Bujinkan Paul, I have heard either Kukishin-ryû/Kukishinden (both of which are 総合武術 Sôgô Bujutsu) or Shinden Fudô-ryû. Both have some connections to Ninjutsu!
Large wooden hammers "Ôzuchi" were also used in squads to smash threw fortifications and gates, so the common Koryû weapons were not the only thing used in battle/attack!
Eric Weil
"Kuji first, Taijutsu last"