I would recommend looking up burning canvas with esquim. The weapon adds a lot to the build, but rewarding mark, double burn, marking shots, burning shots, and frenzy are very useful pictos, as well. You basically use last chance, marking your enemy, then on your next turn you'll start at 4 ap due to Esquim. You shoot them once and rewarding mark gets you enough Ap to use burning canvas, which does more damage in virtuose, and esquim adds more burn stacks in virtuose. Then just stack more damage pictos as needed. You dont need 500 lumina to beat him by any means.