Complex sentence: The series' concept originated in 1999 when Taniguchi was working on "Infinite Ryvius" and wanted to create another series that would contain themes similar to it as well as new ones centered mostly on how people adapted to the 21st century.
Split into simpler sentences: The series' concept originated in 1999 when Taniguchi was working on "Infinite Ryvius". He wanted to create another series that would contain themes similar to it, as well as new ones centered mostly on how people adapted to the 21st century.