Complex sentence: Kudo later encounters an elementary school transfer student Anita Hailey who reveals herself to be the creator of the poison that made him small, and that she too had ingested the poison, but is no longer with the Black Organization.
Split into simpler sentences: Kudo later encounters an elementary school transfer student Anita Hailey who reveals herself to be the creator of the poison that made him small. She too had ingested the poison, but she longer affiliates with the Black Organization.