The Lv.5 gave me the idea that I could make a better "Mana Drain" from the Chain Combo's last 'x', even for additional 0.001%MP regenerations. Because I thought if it basically lets you hit one more target, then the regeneration rate would be (more than) twice the normal.
More exactly, in a 1-on-1, the 4th 'x' "triple-shot" equals 3x(0.001%[actualMP]) and the 5th can vary between 1~8x (depending on distance). But there's supposedly a 9th hit, when I tried the 5th shot on 2 down ennemies, it went to 18 hits.
But it appears that the Chain Combo itself is quite... weird. Or is it that Piercing doesn't have any influence on the process; because above 3 down ennmies, I could have up to 22 hits, no more. While my Piercing is still Lv.1.
Now that we think about it, even a basic Archer's 5th shot can hit several ennemies like the Pathfinder does only by Pierce.
So after this long thinking process, I can say this: 'Shot 1~3' are Pierce-based, 'Shot 4' is a Lv.1 Multishot and 'Shot 5' is a weird "mini-AoE" depending of the distance between the character and the targets.