In the Original timeline, It was actually Future Trunks who used a ability similar to spirit bomb called the sword of hope but what if... What if The Androids' destruction, Goku Black's "judging" the mortals had tainted Trunks' heart just dark enough for him not be able to use sword of hope?

The Fusion Between Son Goku & Vegeta had failed to stop (fused) Zamasu & They were at his mercy Before Zamasu could deal a finishing blow Trunks had managed to stop Zamasu's Ki blade with his own. Both Trunks & Zamasu fought But it was clear that Zamasu had upper hand due to his half immortally & Trunks being slightly blind to anger.

Vegeta knew that if they have hope of winning, They would need the help all they can get & Vegeta reminded Goku about the Spirt Bomb. Goku had forgot about the spirt bomb because Of the Pressure in Fighting Zamasu & Goku Black But Goku didn't waste any time & start preparing The Spirt bomb while Vegeta goes to help His son stall Zamasu.

Son Goku: "I call upon the trees and the water, the sun, the moon and the stars, the plants and the animals. All living things let me share your power." Goku said as his arms were raised in the air.

As if The world itself responded to his call for help, small Kis from the surviving living things begin going where Goku was gathering Energy... But that wasn't enough, Earth's living beings was too small due to the Androids & Zamaus's attacks over the years. Goku knew this so He got further. Goku called out for This Timeline's King Kai

Son Goku: "Say, King Kai, can you hear me?" To his relive King Kai (Future) had responded. "This little bit isn't enough... This isn't enough to defeat Zamasu, But I've already taken all what earth can give! That's why now, i need to gather more energy from the universe! can you let my voice carry throughout the universe?"

King Kai (Future) agreed to help His student even if He wasn't his Goku but it was still His student.

Son Goku: "People of the universe. share your energy with me!" Goku yelled. there was silence for moment then More Kis had began raining down on earth going towards Goku.

(fused) Zamaus had finally beaten Vegeta & Trunks when suddenly He noticed an large ball on top of Goku & it was growing larger each passing seconds as The people of universe(7) send more Ki to Goku.