These additional Riders, aside from Kamen Rider Build are: Kamen Rider Pain and Kamen Rider Roots. These Riders will transform using the World Driver. The series' collectible gimmick are the "Material Bottles", and likely, some of these items will be used for transformation or special attacks/forms.
Lastly, Kamen Rider Build's main weapon is the SaibattoBlade.
[Source: Dukemon of Rangerboard]