Complex sentence: Since their approach was similar to the "Nights into Dreams..." game engine, they requested access to it as a starting point, but its creator, Yuji Naka, reportedly threatened to leave the company if it was used.
Split into simpler sentences: Since their approach was similar to the "Nights into Dreams..." game engine, they requested access to it as a starting point. However, engine creator Yuji Naka reportedly threatened to leave the company if it was used.