Trunks Steps In (トランクス始動 Torankusu Shidō, lit. "Trunks Starts Up") is the three hundred eighty-fifth chapter in the Dragon Ball manga.
Cell continues to scream in pain, having just had his arm and a chunk of his body blown off by Vegeta's Final Flash. Vegeta laughs at his success, and Krillin and Trunks are relieved that he managed to pull it off. However, Cell soon stops screaming and smirks, reminding Vegeta that he has Piccolo's cells, and proceeds to regenerate his body and arm. Cell then walks towards Vegeta, ready to shut him up for good.
In desperation, Vegeta fires a barrage of Ki Blasts, but Cell unflinchingly walks through them and sends Vegeta flying with a punch. Vegeta struggles to his feet, only for Cell to kick him into the air, then follow up with an elbow smash to his back, driving him into the ground and knocking him unconscious.
Cell prepares to put Vegeta out of his misery, but Krillin yells at Trunks that now's the time to step in. Trunks begins powering up, transforming into his Super Saiyan Third Grade form.