Manda is a sea serpent kaiju that highly resembles a Chinese dragon. It first appeared on the coast of Japan in 1961, wreacking Havoc in Okinawa... it took down 4 naval warfare vessles before the JSDF drove it off back to the sea.
However, it continued to assault ships that ventured into a particular area in the south Pacific Ocean somewhere south of Hawaii; this forced the Japanese to use a vessel to eliminate it. This was the Atragon; in the original battle, the Atragon took Manda down with it, Manda never being seen again but the Atragon lost with all hands. But since the JSDF in the Skyverse sent Marq back in time, the event was slightly altered; Atragon battled ferociously with Manda, and with Marq's help, managed to destroy it by using the Atragon's Zero cannon and freezing Manda solid, it's momentum shattering it and thus killing the beast. However, another, similar creature constricted the Atragon, forcing it to take on water and making it sink as it had before time was altered. The second Manda became an ally of Marq, promissing that it would place the Transmitter needed for the Future JSDF to retrieve the Atragon. It seems to have kept it's word, the JSDF in the Skyverse replacined and re-innovated the Atragon.