Azusa only appears in OVA episode 13 and briefly in two episodes of Tenchi Muyo! GXP. Azusa is the father of Yosho, Ayeka, and Sasami. He strongly disapproves of Ayeka's interest in Tenchi, and also greatly underestimates Tenchi's abilities. He is the head of House Masaki, though Funaho rules the house while he is on the throne of Jurai.
In Tenchi Muyo! GXP, Azusa, along with his close friend and Seto's husband Utsutsumi Kamiki, was present at Kiriko Masaki's bonding ceremony. He also appears with his wives Funaho and Misaki when it was revealed that Seina Yamada had become part of Jurai's royal line. And was clearly unhappy about it.
True Tenchi novels
Azusa has the only first generation tree ship in the fleet at this moment, Kirito (Yosho's tree Funaho is also first generation, but at the moment it is currently rooted on Earth, while Tsunami-Fume, which belongs to Sasami, is 0th Generation). Being a first generation ship, it is blessed with enormous power, although not invulnerable. When Azusa fought Kagato his ship was matched against the giant Sōja, and to Azusa's chagrin he found that Kagato was a match for him in power.
Kagato calls upon Ryo-Ohki to attack, and her attack slices through Kirito's Lighthawk wings. Ryo-Ohki's power through its gems could counteract that of the Royal Trees, since both took their strength from the Chousin (Washu and Tsunami, respectively). The clash of energy was considerable, causing a rip in space which Tsunami herself was forced to repair.
Defeated, Kirito was then transported away from Sōja and put near Earth by Tsunami. While there, Azusa saves a young woman from bandits and she helps him recoup from his injuries received from Kagato. Her name was Funaho, the Earthling he would later court and take back to Jurai to be his first wife.