The banner indicates that they have an Aura; which is a bonus they give to everyone on the team, but only if they're in the lead position. Some Aura's have conditions, you have to look in the skills tab to see

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For example, Predator here has a heart Aura, which means if he's the lead, he gies everyone an hp boost.

But if you check under skills, you see it gives a 35% hp boost, but only in arena battles.

So in dungeons, campaign, hydra, etc, he wouldn't give any bonus for being in the lead.

Thank you so much!