Tsunayoshi was rescued by Hibari when he was four years old, and then accidentally became Hibari's pet. Ten years later, Tsuna couldn't remember who the person who saved him was. Later, he fell in love with Hibari, but due to many misunderstandings, he thought he had an unrequited love for Hibari.
This is the parallel world of the original work, a world that can be maintained without the cube of seven, so the Children of the Rainbow all look like adults, but they still have the Vongola Ring.
Moreover, Giotto is Tsuna's grandfather here, and he is also the first generation of Vongola.