The Sword Saint Who Returned from Another World isn't Aware of His Own Abilities: I Came Home After Completing an SSS-Rank Hidden Quest and Became a Level 1 Explorer, but the Swordsmanship I Honed In the Other World was So Strong that the Princess and S-Rank Heroes won't Leave Me Alone

"The Weakest Explorer," Akizuki Yuuta had accepted a hidden quest and was sent to another world. His daily life changed to a very hard adventure, continuously fighting against an endless amount of powerful monsters. And so, when he returned from another world, although he had gone back to being level 1, he had retained his otherwordly swordsmanship skills...! The weakest explorer has become the strongest sword saint! The unyielding warrior returns from another world!

(Source: Kodansha, translated)