Read the chapter. Loki blitzed Imu out of Soru, and shattered his defense after Goofy got bodied by a shield. Lol
I did read the chapter first part loki come down on Imu with his hammer and Imu move.
Then you see loki keep on attacking while Imu moving away and went up to the sky .
We see the ussop speech and then Imu appear and loki was waiting for him .
Loki charge up a huge lightning attack and luffy use it along with hammer .
It broke Imu shield but did no damage to him since we did not see him get harm in any way which is where luffy attack came it .
So at end of the day it took both Loki and luffy to do the damage.
Loki get ridde of the shield but it did not hurt Imu and luffy was with in the lighting and hurt him was his attack.