Receiving Bastion's strong and determined gaze, Leo was filled with relief. Bastion's strength was integral to their plan and one of their lynchpins. Bastion had to hold back two elite guards who were not much weaker than himself and in their prime age. The burden placed on him was unimaginable, but they had no alternative, they were already short on trustworthy manpower.
Bastion knew of the risks but volunteered anyway, given Leo and Luna assurances that he'd be fine. Bastion couldn't go against the magic user who was easily a B-rank mage since he was at severe disadvantage in that match-up. The hope was that Ryuu would be able to defeat the mage and reinforce Bastion before he's overrun. Or if possible, for them to fight the elite guards together in a 2 vs 3 match up. However, there's no way that would happen. Adam knew that Ryuu and Bastion had been working together for decades, their teamwork was impeccable.