Okano's first manga was the one-shot Bakuhatsu! Yuriko-sensei in 1987. The next year, his manga AT Lady won the Akatsuka Award for best comedic story (under the pen name Takeshi Nomura) that lead to a series the next year in Weekly Shonen Jump.
As AT Lady ended, Okano paired up with Makura to start Hell Teacher Nube which after a couple of one-shots became a full series in Weekly Shonen Jump for 6 years. Afterwards, Okano became involved in a few minor projects with both himself and a few other writers such as Digimon Next and pairing up with Makura again for a spin-off of Nube, Izuna the Spiritual Medium.