Tempted to add "odd one out" tag for gameplay reasons, as Bay and Clay aren't obtainable in a single event and their skills don't contemplate each other in battle, unlike the other two pairs.

game2009 said:

Tempted to add "odd one out" tag for gameplay reasons, as Bay and Clay aren't obtainable in a single event and their skills don't contemplate each other in battle, unlike the other two pairs.

You can apply the odd one out tag to other pairs as well, because:

• 777 (left) is a three-members squad, while the others only have two-members (as of this writing at least)
• Dazzling Pearl (middle) are manufactured by Missilis Industries, while the others are by Tetra Line

VR-Man said:

• 777 (left) is a three-members squad, while the others only have two-members (as of this writing at least)

According to a dialogue in the Ark invasion arc, 777 seems to have four members. The fourth one is named Jaune or something.