The tokens are created at the same time as the damage is dealt, since Sekki's ability creates a replacement effect. Since it is a replacement effect, the opponent also won't gain any life for the damage that would have been dealt to Sekki, as that damage isn't being dealt. Instead 20 counters are removed from Sekki (or as many as are possible to remove) and 20 tokens are created.
I have Sekki, Seasons' Guide out and he casts Star of Extinction. Will Sekki make the tokens before or after the damage dealt by star?
Thanks in advance!
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)