Back at the 10th stage of the 3rd dungeon, Yuki was in a heated battle with The Goblin King Final Boss: Atli. After getting hit with the final boss's club, Yuki jumped back before deciding to take his battle seriously.
[Open inventory]
Yuki pulled out "The underworld's holy weapon" which was the bident he had earned after clearing the last stage of the 2nd dungeon. Yuki hadn't gotten a treasured blade from the dungeon so far so it meant that he would get it from the final stage. That of course was only if his hypothesis on how the treasured weapons worked was correct.
In a final attack as Yuki stood which blood pouring all out of his body, he jabbed the bident into the stage floor and began to pour all of his stamina into it without a care in the word if he would drain his body of all the stamina he had which would most likely cause him to pass out and in the condition he was in, most likely die.