This is only the first part of the battle. Unfortunately, defeating the drake does not do the job. You can attack the boss while he is charging his weapon, but pay attention to the imminent attack. This one and the previously mentioned fire attack are the most dangerous ones. The Nameless King will also be trying to hit you and his attacks are harmonized with the drake's - while he is flying around, prepare yourself for lightning bolts hurled your way (it is a good idea to lock the camera on the boss, which makes it easier for you to dodge the attacks), and the drake's diving attack combined with a powerful spear thrust of the Nameless King. As soon as he rises into the air, try to spring up in the direction in which his head is turned (sometimes, it is impossible due to the problems with locking on and camerawork, which is why you should try not to encourage the opponent to attack this way and stay as close as possible. For this reason, try to remain close to Stormdrake and keep him in front of your eyes for the majority of time. In general, the drake is walking on clouds but, if you walk too far away, he rises up into the air and attacks you with a fireball that is nearly impossible to dodge and deals immense damage. Right after you enter the arena, Stormdrake arrives and he is your first opponent. Once the boss starts hurling lightning bolts at you, lock the camera on him, which is going to make it easier for you to dodge at the right moment.

Dark souls 3 storm king