Digimental (V-Tamer 01)

The Digimental (デジメンタル) is an item featured in Digimon Adventure V-Tamer 01 that is related to the Ultra level which exists beyond Mega.

Digimon Adventure V-Tamer 01
The Digimental is unknowingly held by Rei Saiba until her brother, Neo Saiba, takes it from her. It is initially depleted of energy, but Neo uses the energy released when his Alias III fight Taichi Yagami to fill it with power.

It is used to digivolve from his  form to his  one, as well as Zeromaru as  to his.