How to play in Bloodline -1?
In Bloodline 1, lose to the Dark Knight, select 'Save and Restart Castle' you will be on Bloodline -1 with an option to get Dark Mech gear.
Buy as much as you can in the store because there are some of the gears you have never seen before even though you can't equip them in Bloodline -1, but you can put them on in Normal Bloodine once you trash your Dark Mech.
If you have lost to Mech Zero and God King, and you want to give a second try instead of starting on the new bloodline, then follow the following:
1) go to the "menu" button, where you change gear and buy items
2) go to the "option menu" -> character slot-> use another character data->play with it for abit
3) go back to the character slot to use your previously knight who you used but have lost to Final Boss Battle,
4) now you will find your knight is set back to "BEFORE DEFEATED" state