The Cross Heinder is one of Monica Raybrandt's swords in Dark Cloud 2. It's either built up from the Claymore or from the Ruler's Sword and if the Cross Heinder is found, it will only have the "Durable" ability meaning that its Weapon Hit Points (WHP) will go down slower than normally. Its in-game description reads "A treasured, double-edged sword with tremendous power."
This sword, like the Claymore, has the 4-hit combo. It has very high stats but only in Smash and Exorcism if this weapon is found. You can only find the Cross Heinder in dungeon's chests, and therefore, cannot be invented or bought in weapons shops. It's a high-tier weapon (Tier 7) : it'll gain 6 Synthesis Points (SP) per level-up.
The Cross Heinder can only be built up into the Sword of Zeus when it reaches the following stats : 133 in Attack and 135 in Smash, Exorcism, Beast and Scale. You must also defeat at least once a Fire Drake, a Ice Drake and a Thunder Ghost.