What's the point of introducing serena if she gonna die so early. Wtf???????????

Agreed. Why? To trigger ml darkening? To stall their blossoming romance? That character was not needed - they could just show him a grave and say "she died ages ago and the emperor was siply covering that to control you". And the whole shooting her... How the f*ck did he now she was in that house?! And how did the arrow go directly in her heart if she was running from the side? That makes zero sence!!