Kill Elmdor is the sixth optional quest. It is obtained by talking to Biggs located in the northern part of Kalm. The objective is, as one may have guessed, to kill Elmdor. Elmdor is a corrupted samurai wielding a unique weapon - the Fake Masamune, which he may drop upon death. He is located west of the Northern Mountains Waypoint. Upon killing him, the player is prompted to return to Biggs. Biggs will reward you with 1200 EXP and 700 Gold, a special entry about you killing Elmdor is written in the Kalm News and the quest is complete. You can now also acquire the quest Brothers by talking to Izulde in the northmost part of Kalm.
Mae'chen also sells new information for 425 Gold once you acquire this quest. The information is on the optional boss Darianius. It becomes unavailable as soon as you discover Darianius.