Reflection Doubled

Childhood friends Tourma and Acacia go on a perilous journey to a cursed mountain in search of something wondrous. It becomes impossible for them to abandon this quest when the trail isn't what they had expected and they become lost. To make things worse, the path behind them changed as well. What dark force wants to keep them heading up the mountain? Slow build explicit short. (M/M/F, selfcest, threesome, tentacle, 18+)