The first time we are introduced to Guts' sword, the Dragonslayer, in Berserk is in the opening seconds as the master blacksmith Godo mends it. The first time we are properly introduced to it however is when Guts cleaves a brigand clean in two, taking out a solid wooden table and most of the floor with him. It's a monumentally absurd weapon, as tall if not more so than the wielder and likely just as heavy, outside of fiction it would be impossible for any human to wield.
For the 1997 anime at least, this introduction is misleading as the sword that we see for the remainder of the series is just as tall but not quite as absurd. It's not the only one of course - Guts grows up and events transpire which changes who he is and subsequently what he wields.