Yu-Gi-Oh! 5D's - Season 1 Episode 142

As Jack, Leo and Luna struggle to survive, Aporia summons his key monster, Machine Divine Emperor Dragon Asterisk which will inflict 1000 points of damage to anyone who tries to Synchro Summon. Lamenting that he hasn't been able to protect anyone, Leo risks some of his own life points to protect Jack and Luna and weaken Asterisk. Leo then summons Power Tool Dragon and Ancient Fairy Dragon and gets hit by the 4,800 points of effect damage, bringing his life down to zero, causing him to die. The shock of Leo's death puts Luna in a critical state, as her life points gradually starts to drop, as her pulse weakens. However, Leo comes back to life with 100 life points, thanks to Ancient Fairy Dragon, and his Morphtronic Lighton's effect, and becomes the sixth and final Signer, with the Mark of the Crimson Dragon's Heart.