Chill your glass (quick rinse with ice water or park it in the freezer for a minute).
In a shaker, add gin, lemon juice, blood orange juice, and simple syrup.
Add ice and shake hard for about 10–12 seconds.
Strain into a champagne flute (fine strain if you want it extra clean).
Top with champagne (slowly, unless you enjoy cleaning up your own bad decisions).
Garnish with a blood orange wheel or lemon twist.
Optional: add 2 dashes bitters or a tiny pinch of salt to deepen the flavor and sharpen the “danger” vibe.