While samurai did not have something that was exactly similar to warhammers, Feudal Japan DID have variations of yari that had different areas of proficiency. e.g. the Jumoni Yari, which had three points: One in the middle, and two that were slightly curved beside the middle spike, the Sankaku Yari, which did not have a blade, but instead had a strong point like an awlpike that was meant for penetrating armor, etc. They also had the Kanabo, which was a heavy club of iron that had spikes, and was around 2 meters long, and the Otsuchi, which was a warhammer, but not in the European sense which goes by different names (European one also goes by poleaxe, lucerne, crow's beak, etc.) The Otsuchi was pretty much an actual large hammer meant for war. While they may not be the exact depictions of weapons you were looking for, they did serve their different purposes: Different spearheads, bludgeons, for different things. This may be due to their armor-- When compared to European full plate armor, surviving examples of Japanese armor have noticeable gaps that are at most, padded cloth. There are also some parts left open, like the sides of the neck, which I infer is probably due to the samurai's past use as horse archers, which meant a bigger need for being able to turn around, look up and down, and more visibility in comparison to the visors and gorgets of the European knight. They even had a dagger for this, which was called a Hachiwari, which was used about the same way as a rondel dagger for Europe (insert it into the gaps of Samurai armor). The unprotected gaps in samurai armor probably kept slashing weapons relatively valid even throughout the Sengoku-Jidai, which shows in their use of different spearheads and naginatas. Even spears that were pointed, and not curved, had very large heads for slashing through. Hopefully this helps. Source: "The Samurai Warrior" by Ben Hubbard.