Cant believe touhou music slipped my mind. Though I'd have to say for me it's a toss up between
YouTube - SA Stage 6 Boss - Utsuho Reiuji's Theme - Solar Sect of Mystic Wisdom ~ Nuclear Fusion
and
YouTube - Bloom Nobly, Cherry Blossoms of Sumizome ~ Border of Life -- Yuyuko Saigyouji's Theme