I've only recently started this part of F/GO, but supposedly it's possible to validate the use of forces beyond what humans are meant to handle through Ordeal Calls. Theoretically, that means HSR characters could one day prove that they can wield magic. Mixing worlds produces many interesting paths.

The Holy Grail itself is also what's known in Fate as the "Third Magic," materialization of the soul, one type of true magic. Generally, reaching magic corresponds to reaching something called the Root, which also triggers the Counter Force. Just know that it's considered a crime against humanity.

On a more serious note, Oti pulling a Holy Grail into #HSR could've turned out to be a world-ending event. The Counter Force typically doesn't get involved unless there's a real threat determined by the collective unconscious of humanity (see how the world itself summoned Servants in F/GO).

Of course I also lost and went to hard pity on the light cone. This is why we save, folks.

First one hard pity after losing to Seele...