Multiple popular themes converged: Modern Day Dungeon, Weak to Strong, Kicked Out of Party / Family.
The story background is modern-day Japan, where dungeons appear in many different places. The MC was struggling to make ends meet due to he was kicked out of his family. The reason was that he was weak and had no skill. In addition, his engagement was broken off. However, unbeknownst to others, he was a late bloomer. He got his skill on his 18th birthday. From then on, he uses his skill to train in a pseudo-dungeon and level up. He also gained multiple skills during his training. At the time of this review, MC is still in training, but has leveled up nicely.