Lerahk is poison, and I mean it!
~ Takua referring to Lerahk

Lerahk was one of the six Rahkshi that were released by the Makuta to stop the Matorans Takua and Jala from finding the seventh Toa.

BIONICLE Mask of Light: The Movie

Lerahk was released by the Makuta along with Panrahk and Guurahk to stop the approach of the seventh Toa. He and his fellow Rahkshi attacked Ta-Koro in search of the Kanohi Avohkii (the Mask of Light). He was hit on the head by Turaga Vakama until Tahu decides to face him. Lerahk scratches Tahu's mask infecting it with poison which did not kick-in until later. Lerahk then escapes from Ta-Koro by using his staff of poison to fly.

Lerahk later returns with Panrahk and Guurahk at Ko-Koro and is then frozen in a lake shortly after by Toa Kopaka.

However, the ice did not hold him and the other Rahkshi for long and he returns to fight the Toa. However, he, Panrahk, and Guurahk end up being frozen in a mix of elements created by the Toa.