you went out exploring to find Regigigas, so you went to capture all the regi's to awaken him...and eventually you reached his cave, and....Regigigas was slumbering in his cave... laying there...snoring quite Loudly, till he randomly awakens.

"ZUTT ZUTT...."

he says while standing up, and controlling the legendary titan's that you brought to him, and staring you down.

"REGIGIGAS."

he says, his voice echoing through his cave.