Asura is a mode, but Zoro only uses it for one attack
not sure if it takes a bunch of Stamina from him so he keeps it for last
But it’s a mode because he uses different attacks
hell memories on other hand is ambigeous
The attack itself is called hell memories, so it can be a technique
but he also covers his whole body with fire which should allow it to be a mode to use different techniques but Sanji doesn’t do that
it’s weird… maybe as Sanji stated
His body wasn’t able to withstand more heat before to make the Ifrit jambe.. which leads us to conclusion
if Sanji’s leg (his strongest part) couldn’t handle more heat and fire before… then rest of his body including his precious arms and hands… they will be vulnerable for hell memories to be an elongated mode… because his legs might withstand the heat but the rest of his body cannot contain such heat for longer than one attack
however, with exoskelton… he might now be able to stay covered in flames as a mode!?
who knows
but we can be clear now that heat/fire is affecting Sanji unlike mera mera fruit where Ace or Sabo don’t feel the heat
Sanji feels the heat, but he doesn’t burn because his heart burns hotter and his body can tank and endure such heat
and now with exoskeleton combined with CoA, he can withstand a hotter flame, thus we got ifrit jambe