Hey judge, If I have Ahri, Confident on the battlefield and my opponent attacks with a 1 Might unit, will Ahri, Confident still trigger and gain +1 Might, even though my legend (Ahri, Nine-Tailed Fox) says "give it -1 Might, to a minimum of 1 Might"? In other words, does Ahri, Confident still trigger even if the attacking unit's Might can't actually be reduced?

Radiance rules aren't published yet. This uses the printed card and current rules only, and it isn't a ruling on the new mechanics.

No — against a 1 Might attacker, Ahri, Confident does not trigger, because no Might is actually reduced. Ahri, Nine-Tailed Fox's -1 "to a minimum of 1" on a 1 Might unit is snapshotted as -0 (rule 479.4.b), so the unit's Might never comes down by 1 or more. Ahri, Confident's second ability reads "When you reduce the Might of an enemy unit here by 1 or more, give me +1 [M] this turn" — with an applied reduction of 0, that condition isn't met, so she gains nothing.

The distinction that matters: it's the applied reduction the ability checks, not the nominal "-1" on the legend. If the attacker has 2 or more Might, the legend reduces it by a real 1 or more, Ahri, Confident triggers, and she gains +1 Might this turn. Note the damage-style "treated as 0" clause on negative Might doesn't help here — that's for combat/damage math, and snapshotting means the reduction is tracked at 0.

This is my interpretation based on rule 479.4.b (snapshotting) and the printed card text. No official FAQ exists for this specific interaction.