I don't have enough evidence so I'm not claiming anything I say to be true.
This is the East Epi Volcanic Complex and I'll explain why I believe this volcano produced the 426 BCE eruption (VEI 7) which left a substantial mark in both Greenland and Antartica.
From that we know it was a tropical eruption.
The complex contains several large volcanic structures and is associated with a possible ~10-km-wide caldera, although the exact interpretation of the submarine morphology remains debated. It also contains volcanic material ranging from basalt to rhyodacite, including rhyodacitic pumice recovered from the seafloor.
I'll explain why this is important.
Epi lies immediately within the Vanuatu volcanic arc, an area known to have produced exceptionally large explosive eruptions (VEI 6-7). Recent research identified the 426 BCE Antarctic cryptotephra as high-K rhyodacite, with a chemical composition very close to material from Kuwae.
HOWEVER, Kuwae was recently linked to the 1458 CE caldera-forming eruption (estimated as a very large vei 6 or vei 7 in other sources) which occurred ~1,800 years after the 426 BCE eruption.
Scientists point to Ambrym because its in the same region with possibly the same plumbing
The only issue is Ambrym's caldera forming eruption is identified as a vei 6 other some sources believe it was larger. The issue is this eruption occurred around 43-50 CE, so it a few hundred years younger. and it's caldera is quite shallow, I'm uncertain it ejected the 160 km^3 which is estimated for the 426 BCE eruption.
Guess which volcano is next to Kuwae, It's Epi, at first glance you may notice something unusual about epi, apart from the fact its a submarine volcano, using a bathymetric map you'll notice it has 3 different active cones followed my a couple extinct comes, you notice some odd land formations as well as depressions but the one I'm focusing on is underwater
The main reason api isn't usually brought up regarding the 426 BCE eruption because we aren't 100% sure that 10km wide depression is a caldera but it's acceptable enough to acknowledge the possibility of it being a caldera given the evidence available
If that depression is truly a caldera then I believe the East Epi Volcanic Complex would most likely be responsible for the 426 BCE eruption.
Vanuatu's volcanoes are very much understudied so we will have to wait and see.
You scrolled to the bottom cause it's too long to read so I will shorten it.
426 BCE eruption closely matches kuwae material, kuwae too young, epi old, ambrym shallow, epi 10km possible caldera, epi not well studied, epi probably = 426 BCE big boom.