The World's Fastest Level Up (Manga) Vol. 3

Following a dungeon collapse, Rins former party, the Kings of Unique, makes the rash decision to take on an overpowered final boss. When Rin realises that amateur adventurer Rei is also with them, he decides to try and save her, even if it means revealing his unique skill to the world. Theres one thing Rin doesnt consider, though, and thats the strength of the final boss itself. When worse comes to worst, can Rin take it on solo?