开心超人联盟之超时空保卫战

After Zai Zaijia goes missing, Xiao Zai attempts to build a time machine based on the blueprints left by his father. After many failed attempts, he finally realizes that the completed time machine can only travel to points in time when the time machine itself existed. Twenty-five years later, Happy Superman accidentally discovers the time machine and inadvertently travels back to when Dr. Zai was a child. Due to the time machine's unique limitations—it can only go to the past—and because young Dr. Zai is lonely and friendless, the Supermen decide to stay in the past. Posing as older siblings, they care for Dr. Zai, helping him become more cheerful and learn to take care of himself, while also searching for a way to return to the future. At the same time, they must confront the mischief and destruction caused by Big and Little Mighty, along with other monsters.