Complex sentence: He began to haunt Kohina after seeing how she lives as a'doll' and wanted to help her live better as her current life wasn't suitable for a young girl to grow up in and thus became her legal guardian.
Split into simpler sentences: He began to haunt Kohina after seeing how she lives as a'doll,' and he wanted to help her. Convinced that her current life wasn't suitable for a young girl, he became her legal guardian.