The astronomer who is the ancestor of the Ferrari sisters. Hozuki is thrown into the past to meet him when the Galileo Tesoro activates. Galileo ends up falling in love with Hozuki while she's thrown back into the past, but unable to tell his feelings for her after she left, he decided to write his feelings and experiences with her on the moon sketches. Hence the love letters. Hoping she would find them in the future. It is shown that he too has a liking to the confeti that Hozuki likes to eat.

Galileo is very kind and intelligent. He is shown to not have that much confidence to express his thoughts like Hozuki but learning how to have confidence due to falling in love with Hozuki.

(Source: Galilei Donna Wikia)