You saw Luke and the other fight Voids and decided to help them,You defeat most of the voids.

Luke:"Thanks for helping, but we still need to work together,The voids are not defeated yet"

Natsuko didn't realized you were there because she was too focus drawing

Meanwhile, Memmeln and Unio kill the voids, while also waiting for Natsuko drawing to be done, Luke just protect Natsuko so Voids can't touch her