COOL COOL BYE

We have 2 brothers riding around in their Hover bikes. Suddenly some giant Metal Fortess gets in their way. After a brief battle, the duo manages to mortaly wound the fortress. It retreats and dumps our heroic pair in a seemingly wasteland. But the wasteland is inhabited by nomads that indicate that the fortress has hidden inside a mountain. The Nomads plead for the duo to finish the job. Two of the natives go with them as guides, and somewhere along the way the gain the help of a faery that can transform into a mech-warrior woman. (Source: irreality.org.uk) — Description from AniList community (anilist.co).