Does Sett The Boss's effect initiate a chain, and can you respond to it with a reaction effect?

Ruling: No, Sett The Boss's effect does not initiate a chain and you cannot respond to it with a reaction effect. It is a passive replacement effect.

Nuances:

• Replacement effects in Riftbound intercede while something is resolving and modify its outcome; they do not create their own chain link
• Sett was errataed from "when" (which is a trigger word) to "if a" (not a trigger word)
• The exhaust symbol is only used in costs of activated abilities, which is why Sett uses text instead of the symbol