What is the order of resolution of abilities during the damage step?
The official English rule states: Official reference guide


  When defending player receives damage and reveals their damage card, if the card is marked with an EX icon in the top right corner, the player triggers the card's EX Burst and may immediately apply the effects of the card. ...


Therefore here it goes:


Lightning is not blocked and produce damage.
The Ex Burst is triggered.
Then Lightning ability is triggered dulling a forward.


Note that you can't counter Ex Burst. However, auto ability or field ability can be countered.