Master Sinden:
I possess the fourth Resonance Amulet.
Long ago, when Panacea blocked the path of this pilgrimage, he confronted her with his brother. The brother, the Starlight Knight Kastien, who was a Mother Tree Guardian, supposedly agreed with Panacea, but he gave me the Resonance Amulet, saying that it was not our place to block the pilgrimage that was ordained by the goddess Eva. At the same time, he created a seal that would allow its use only when helping another race...
That seal's key was broken in two and the pieces were given to a group of petty Orcs and the Silenos. They eventually became the Ketra Orcs and the Varka Silenos. Thus, you cannot obtain the key without befriending them.
So, pilgrim, which side will you visit?
Ketra Orcs!
Varka Silenos!