Complex sentence: As he flies her and Boh back to the bathhouse, Sen discovers that when she was little, she fell in the Kohaku River but was washed safely ashore, and realizing that Haku is the spirit of the Kohaku River, Sen tells him his name.
Split into simpler sentences: As he flies her and Boh back to the bathhouse, Sen has another memory of being underwater: when she was little, she fell in the Kohaku River but was washed safely ashore. Realizing that Haku is the spirit of the Kohaku River, Sen tells him his name.