Yuukyuu no Gusha Asley no, Kenja no Susume

From J-Novel Club: A couple of thousand years of solitude would wear down any young man, that is, anyone except Asley, an eternally youthful and eternally foolish sorcerer. After all, he has man’s best friend... er, familiar, to keep him company. When his Level 100 canine companion Pochi demands that he get some fresh air for the first time in two centuries, Asley sets out to reintegrate into society and test his magic mettle. His mission? Dropping several unglamorous titles from his repertoire and restoring his good (okay, decent) name. A brand-new world and fresh adventures await Asley after his many years of hermitage. Perhaps he’ll lend Pochi a hand to place first in the mysterious Familiar Feud. Or maybe he’ll lose all vestiges of dignity and turn tail. Whichever comes first! No matter what, Asley has great evil to fight, a big world to save, and even a little growing up to do. That is, if he can endure Pochi’s “friendly advice” along the way. Official JP: Comic Earth Star, Official channel of Comic Earth Star in Nico Nico Seiga, Pixiv Original webnovel: Shousetsuka ni Narou