my interpretation is that the child who made the bookmark was actually Xeno himself as a gift to Baron while as a part of the "Blue Institute" the reason Baron is asking "Who am I?" in Xeno's dreams is that likely when they were taken into the institute they also lost their original identities meaning Tomohiro and Kinou are also further aliases, but Baron took to that knowledge badly and always questioned his origins.
Off feeling the purpose of the Blue Institute was to create highly specialized prodigies in certain fields