Chikyuu no Kaijuu

To protect the Earth from space monster invasions, 52-year-old Daikichi Oogami must turn into a giant and fight the odd-looking creatures off. However, he has now become a laughingstock, and his battles are viewed as entertainment by many. His son, Daichi, is frustrated at how his father's struggles to safeguard humanity are belittled and underappreciated. Wishing for everyone else to take these battles seriously, Daichi resolves to become a hero. [Written by MAL Rewrite]