The only love interest(s) locked by a gender wall are Parker/Fnoob because they share the same character sprites as the protagonist, so essentially, we wanted the player to avoid dating "themselves"
By default/route wise you can only be duo partners with TwinTails and either Parker/FNoob depending on who you pick as your MC. If you'd like to romance Striker, Holly, or Midnight you'll need to go solo for their storyline to begin but this is regardless of what gender you choose at the start.