Tamitaya is a magic spell that is compulsorily cast on weapons and even farm tools so that when used, it would not harm or kill monsters or people in the process. The Tamitaya's magical effect has appeared in all Rune Factory games so far, and first mentioned by Mist in Rune Factory: A Fantasy Harvest Moon.
Tamitaya is known as 'Retornen' in the first and perhaps in a few other English releases of the game, but in Rune Factory 4 it is called Tamitaya.
Upon a weapon or farm tool is crafted, Tamitaya is cast on them in motive to prevent the weapon from actually harming monsters so that upon their defeat, they may be sent(or teleported) to the Forest of Beginnings safely. Tamitaya's magical effect will stick to the weapon or farm tool, until they are completely destroyed. Tamitaya's magical effect is responsible to send the monsters to the Forest of Beginnings. However, there are some monsters, such as the Arch-Dragon , that can go to the Forest without the aid of the Tamitya spell.
Weapons or farm tools with Tamitaya's effect also works on humans, but the effect is only limited to not harming them, nothing else.
In special cases, such as when you defeat bosses and they show the boss meeting a terrible end, it is unknown if Tamitaya is still effective.