Even if a unit has Strike-first, most units that can fight two times in a single combat phase gain Strike-last after the first fight ability concludes, preventing any shenanigans. However, I believe I found a weird interaction.
Varanguard have this standard 2 fight ability Relentless Killers: “This unit can use 2 Fight abilities this phase. After the first is used, however, this unit has Strike-last for the rest of the turn.”
Abraxia has this passive: “If a friendly Varanguard unit uses the ‘Relentless Killers’ ability while it is wholly within 12" of this unit, that unit does not have Strike-last as a result of that ability.”
Belakor uses his “Deadly Trap” ability during the enemy’s combat phase and successfully gives my Varanguard and himself Strike-first for the rest of the turn.
Begin Fight sequence.
I get to activate first because I have Strike-first units and my opponent does not. I activate Varanguard and they fight. Normally, they would have Strike-last now cancelling to “Strike-normal.” Because of Abraxia they do not have Strike-last and therefore keep Strike-first.
Normally this would still not work because 19.0 “After all those Strike-first units have fought, the active player picks the next unit to fight. However, I have two Strike-first units and Belakor still hasn’t fought yet.
So now I pick Varanguard to fight again, they have Strike-first so they are not included in the Strike-first rule that says “other units cannot use a Fight ability until those units have been picked to use a fight ability.”
Finally, Belakor fights, causing all units with Strike-fist to have fought and allowing the active player to pick the next unit to fight.