Reboot Cheerleader

You need to obtain additional copies of the same character card or use specific promotion materials. If you collect them step by step, the number of stars will increase. Don't be too impatient.

Are you referring to the <Candy Bracelet> with that star equipment? You have to do it through awakening. You can summon 4 if you have the normal awakening "Concentrated Summon" (additional summon of 2 Happiness Crystals). I don't have the legendary awakening "Mass Summon" (doubles the number of Happiness Crystals summoned), so I'm not sure, but it might work since it says 'doubles summon count'. Also, awakenings do not apply to the Reboot normal story (Heroes, Attack of the Zombies) and only apply in the Rupture of Doom mode.