|Because this Kaiju / Seijin is a character in the show instead of the monster of the week, it has been given its own page. If you're looking for the original page, see Alien Mefilas.|
"The man who laughs last is the one who has the trump card. There are cards of light and darkness throughout the universe. Juggler has six powerful Lord Monster cards and we're gonna take it from him."
- ―Nostra as he plotted to betray Jugglus.
He was first heard onscreen at the beginning of episode six of the show (but not seen) discussing to his fellow members, Alien Metron Tarude and Alien Nackle Nagus, about how to deal with Earth before Jugglus Juggler showed up to volunteer to deal with Ultraman Orb. After the Ultra defeats Aribunta, Nostra finally reveals himself in person and thanks the once good person for using the Super Beast's card to save Nagus. After the latter leaves, it is revealed that he is in possession of Ultraman Belial's Ultra Fusion Card, to which he refers as a "trump card" to use as a last resort, should Juggler betray him and that he plans on taking the Kaiju Cards of the Lord Monsters from him to use them himself, not knowing Juggler is listening in.
Seeing how Orb's strength comes from humanity's trust and support, he called forth the Space Directive M774 Alien Babarue Babaryu to impersonate as Orb but the plan failed when Telesdon randomly appear in the city, causing him to leave Babaryu to fend for himself, which backfired the supposed plan of impersonation. When Babaryu refused to serve them again, he had Juggler summoned Cherubim to take care of the traitor before the real Ultraman Orb appeared and saved him.
Nostra soon gives Juggler the order to kill Ultraman Orb and took his possession of Ultra Fusion Cards, in exchange of Ultraman Belial's card. Giving Juggler Nagus' Black King card, he arranged this matter to have Juggler killed to claim his Lord Monster cards by sending Nagus to do the assassination. Although failed to kill Orb, the acquirement of the Lord Monster cards was enough to satisfy Nostra, having stated that he would never agreed to hand over Belial's card. To his disbelief, Juggler survived his assassination with Bemstar's card and killed his employers to reclaim his cards, as well as taking away Belial's card. In his last breath, Nostra curses upon Juggler before exploding into pieces.
After the deaths of Nostra and Nagus, the Union's ship is now in possession of Tarude, who sought revenge on Juggler upon his master's death.
- Powers and Weapons
- Belial's Ultra Fusion Card: Don Nostra is in possession of Ultraman Belial's Ultra Fusion Card, to which he replied as an ultimate trump card. How he obtained the card or how it works is currently unknown, but it is believed to be functioned like Gai with Ultraman's card. Ironically, before he would put the card to use, he was killed by Jugglus in his true form.
- Kaiju Cards: Shared with other Planet Invasion Union members, Nostra is also in possession of Kaiju Cards, despite never shown to use them. For a brief moment, he is in possession of Jugglus' Lord Monster cards until the former reclaimed it upon his own death.
- Saucer: Don Nostra and the Planet Invasion Union's main transportation is a conjoined saucer, which was the same model as the first generation Alien Metron. The saucer itself has the dimensional distortion machine that traps its victims within space time continuum, although it is revealed to have a leakage, as SSP and Shibukawa used it to escape.
- Grip Beam (グリップビーム Gurippu Bīmu): Like his predecessors, Nostra can shoot blue lightning from his right hand.
- His voice actor, Hiroki Yasumoto, previously voiced Surai in Ultra Zero Fight and Ultraman Retsuden, were Yasumoto remarked if he is fated to voice Mefilas and his future generation's.
- Nostra saying that there are certain beings who would foolishly sell their own planet is a reference to his first Generation trying to force Isamu to surrender Earth to him before he admits his defeat by the original Ultraman.
- Him leading the Planet Invasion Union is based on how the First Generation from Ultraman was supposed to have a group of alien allies, until the idea was scrapped.
- Nostra's cape is a reference to the Demon King Mefilas from Ultraman Super Fighter Legends manga and OVA series, who was voiced by Nobuyuki Hiyama in the latter media.
- Nostra's name is derived from the phrase, 'Cosa Nostra', Italian for "Our Thing". This phrase is commonly used by members of the Sicilian Mafia to discuss their operations in secret.