Ultraman Tiga: S1 E11 - Requiem To The Darkness Ultraman Tiga

Horii arrives to an area where he detected a mysterious life signature, and ends up reuniting with his best friends from college Ryusuke and Sayaka. However, Ryusuke is acting strange. Horii discovers a signal for the Monster Catcher he shot inside the monster coming from Ryusuke's body, deepening Horii's suspicions.