Going off of what Thominator said, I agree that this is likely about the birth of his child.
As others have said the word "kawaii" is typically used to mean "cute" but it has other meanings. It can also mean "innocent" and "childlike." So I would say that his lyrics about freedom and losing their world is referring to growing older, losing your childlike and free attitude as well as your innocence, but with the new arrival the kawaii feeling will return to their lives.
Going off of what Thominator said, I agree that this is likely about the birth of his child.
As others have said the word "kawaii" is typically used to mean "cute" but it has other meanings. It can also mean "innocent" and "childlike." So I would say that his lyrics about freedom and losing their world is referring to growing older, losing your childlike and free attitude as well as your innocence, but with the new arrival the kawaii feeling will return to their lives.