I think Ranta mostly acts the way he does because he feels their lives aren't in any real danger as long as they are in a group. But when Deathspot showed up he realized that thing along could wipe out the group so he did everything he could to make sure they all make it. The group never has never seen this side of him because there was never a need to show it. Sure his communication skills need word but he demonstrated he doesn't need to talk to know what the others are doing in combat as was shown when he and Haru fought together.