Broly becomes enraged by his memories of Goku and with that rage, his strength rises. He uses this technique several times in his two movie appearances, Dragon Ball Z: Broly - The Legendary Super Saiyan and 'Dragon Ball Z: Broly - Second Coming.
Appearances in games
It is first introduced as a Blast 1 in the Budokai Tenkaichi series and a Super Attack in Raging Blast games. When it is used in the Budokai Tenkaichi series, it puts Broly into MAX power mode, and his Attack, Defense and Ki strength go up. When used in the Raging Blast series, he is unable to flinch and his Attack strength goes up.
Broly also uses this technique in Dragon Ball Z: Attack of the Saiyans to raise all of his stats: Attack, Defense, Accuracy, Evade, and Speed.
In the arcade game Dragon Ball Heroes, using several versions of Broly together can use a combined Kakarot! to raise their powers.
"Broly's Z-Soul. Attacks received do not cause stagger until Health lowers to a certain level."
— Dragon Ball: Xenoverse Z-Soul in-game description
In Dragon Ball: Xenoverse, it appears as Broly's Z-Soul Kakaroooot!! which can be equipped by the Future Warrior. When the Z-Soul is equipped it increases the users health stat by 2 and Basic ATL stat by 5 though decreases both Strike Supers and Ki Blast Supers by 4. It also prevents the user from staggering when attacked until the wear's Health lowers to a certain level. The Kakaroooot!! Z-Soul can be obtained in Parallel Quest 51: "Heated, Furious, Ultimate Battle".