Future Trunks charges a Future Kamehameha
Future Kamehameha is a technique used by Future Trunks. It's his version of a Kamehameha. He used it for the first time while training with Vegeta. Trunks wanted to use a powerful technique so he made up his own variant of the Kamehameha. The attack caused some damage to Vegeta in his base form. Later, Future Trunks used this attack to blast a hole through Future Yakon, and later against Majin Buu. This time it had no effect and Future Majin Buu absorbed him.
Future Kamehameha
There is also a rapid-fire version called Continuous Future Kamehameha.