Who does Lebusi Shu refer to?

Being happy and reluctant to think about Shu refers to Liu Chan.

The protagonist of the idiom "Be happy to miss Shu" is Liu Chan. In 263 AD, the Kingdom of Shu was defeated by the Kingdom of Wei. Liu Chan voluntarily surrendered and took some old ministers to defeat the Kingdom of Wei and became Duke Anle. One day, Sima Zhao, the general of the Wei State, invited Liu Chan to dinner. During the meal, he deliberately asked people to perform Shu's acrobatics, hoping to humiliate these people who came from Shu.

The old ministers were very sad when they saw these Shu's acrobatics, but Liu Chan clapped his hands happily. Sima Zhao deliberately asked Liu Chan sarcastically whether he was happy here and whether he missed the Kingdom of Shu. Liu Chan said that he had plenty to eat and have fun here, and he would not miss Shu at all. Later, everyone used the phrase "lucky and reluctant to miss Shu" to describe a person who was so happy that he forgot to go home!

Original text of "I'm happy but don't think about Shu":

The king asked Zen: "Do you think about Shu a lot?" Zen said: "I am happy here, but I don't think about Shu." But when he heard it, he asked to see Zen. He said: "If the queen asks, it is appropriate to cry and answer: The ancestors' graves are far away in Long and Shu. She feels sad in her heart and thinks about it every day. Because she closes her eyes." The king asked again, and the answer was as before. The king said: "What? It seems like the right words are wrong!" Chan looked at him in shock and said, "It's just like your command." Everyone on the left and right laughed.

People often refer to people who are so happy that they forget to return, or who are so happy that they forget their origins and have no thoughts about their homeland. This is called "being happy but not thinking about Shu". It is a metaphor for having fun in a new environment, being content with the status quo, being nostalgic for a foreign place, forgetting your hometown or not wanting to go back to your hometown at all, and no longer wanting to go back to the original environment.