Yūrei

In the past she was a small Eevee that died with her family in a massacre that she could never solve. When it awoke it did so as a Gastly without many memories of its past life, but, for some reason tied to the bones of its former self, and at the same time trapped to stay in that mountain until a small group arrived. In order to leave the mountain she was able to make a deal with one of the members of the group (Blitz) and they tied their souls together so that Yūrei could finally leave the mountain. Now she travels with this small group