As ever, no such thing as a free lunch in this story.
āHe was able to use Kindness in rapid succession because that protective wall existed. So it was like giving aid to oneās enemies, though Iām sure she hadnāt intended thatā ā this seems to have intentionally been left vague in the original. So who is āherā in this case and where did this āprotective wallā come from? Given that Reise refers to āherā specifically and āgiving aid to oneās enemiesā, this couldnāt be D or Sariel. So the only other āherā known to be capable of doing such a thing and who would be regarded as an enemy is Shiro.
So what is this protective wall and where did it come from? If you refer back to chapter 246, we see this: āThe little trick Iād prepared earlier was for protection on senseiās soulā. This was a protective barrier Shiro put around Oka-chanās soul to prevent Potimas from infesting her soul again with his soul parasites. Itās possible that Shiro applied this protection to others, though I canāt find a direct reference.
Perhaps the more likely explanation is due to Shiro intending to protect the reincarnators and some others when she collapses the System. In chapter 269 Shiro says āI will expand the Systemās soul sheltering functionality, improving it so that at least the reincarnators can be saved.ā We never get the details of how this was implemented though, but given that it is something intended to survive the collapse of the System itās reasonable that Shiro set up something in advance to protect or reinforce the souls of certain people. If so then Reise is saying that it also helped Shun use Kindness in rapid succession and without it Shun would have collapsed much sooner and perhaps have already destroyed his soul. This would also mean that if/when the System collapses that Shunās soul would also collapse.