Complex sentence: When Kohaku and Rin were taken to the Underworld, he goes after them and Rin dies from being in the realm for too long before Sesshomaru's mother revives her with the Meido Stone Inu no Taisho gave her.
Split into simpler sentences: When Kohaku and Rin were taken to the Underworld he goes after them. Rin died from being in the realm for too long before Sesshomaru's mother revives her with the Meido Stone Inu no Taisho gave her.