Each boss fight is badass, but among them there is a couple that has crowning moments of awesome. For example, yuyuko and the cherry tree going semi-berserk and forcing a reflowering without the needed amount of spring, and giving one of the most brutals spellcards ever is one of such moments. Another was when shinki was losing the fight against the protagonist of mystic square and uses all her power in a heavy bombardment skill, latter known as devil incantation, burning the makai itself with the attack.
In this case, I picture miko being almost defeated and the divine spirits in the mausoleum coming down in a shooting star shower way, making up for the miko last stand against the protagonist. In all touhous fights, this is one of my favorite moments ever, and I praise and respect zun for being able to convey such emotions in a danmaku game