Isso pode ser Yamato Takeru
A million years later, the Death Star Yomi is approaching the Onam System once again. Tsukuyomi, the master of Yomi, plans to take this opportunity to realize his dream of ruling the entire universe. He is desperate for the last stone containing Yamatano Orochi. If Tsukuyomi can get hold of this stone, Yamatano Orochi will return to life and its power will become his. Tsukuyomi needs Sky Warrior Susanoo to capture the stone, and sends 8 Sky Soldiers to get Susanoo back. But it is too late. Susanoo no longer belongs to Tsukuyomi. It belongs to Takeru, a 13-year-old boy from Earth, who happened to discover the buried robot Susanoo and woke it from its million-year-long sleep. Takeru becomes involved in the battle against the Sky Soldiers and their evil master, Tsukuyomi. Susanoo stands up to protect his friends and their planet.
A abertura não mostra ele convocando o robô, mas você pode ver a flauta (mais uma ocarina) em suas mãos, e a espada mais tarde.
Ah, e é uma ocarina:
Tamanoo is initially piloted by Amatsumi but after he is killed by Kiriomi, Yamato's new friend Kaon tries to pilot it. Even though Amatsumi was dead, Tamanoo is still shrouded in his evil presence. Only through Yamato playing his ocarina is the evil presence destroyed and Kaon is able to pilot it.
Você pode ver o Yamato usando-o no segundo episódio:
Eu encontrei pesquisando anime boy convocando robô com flauta , o que me levou a uma consulta no Reddit onde foi a resposta, então eu pesquisei mais detalhes.