"You never cease to amuse me, it's been ages since I laughed so hard at anyone but a fool. But unfortunately, I have had but one comrade, and he is all I shall ever have."
"He who was my companion, through adventure and hardship, is gone forever."
― Jean-Luc Picard (Star Trek)
"Greater love has no one than this: to lay down one’s life for one’s friends."
― Jesus Christ (John 15:13)
"I will be loyal to the end. And beyond."
― Isaac confirming his loyalty to Dracula (Castlevania)
"Doesn't matter how many of us die, so long as he stays alive...The Hi Shin Unit will never die."
― Den Ei on his captain, Shin (Kingdom)
"Whenever you found yourself unable to go on, I'd take you onward myself. Carry you if I had to. That's what I've done up to now, and I'll keep on doing it. Forever, until the day you die.""
― Renji Abarai (Bleach)
The ability to remain completely loyal until the very end. Sub-power of Indomitable Will.
Loyal to the End
The Loyal Knight
The Loyal One
User can remain completely loyal until the very end, either using it on others, making them completely willing to protect and never abandoning the user or use this on themselves, making them unable to abandon or betray their loved ones if they're ever in need.
Create an army of soldiers who will never abandon or deceive you.
Rider (Fate/Zero) possesses Ionioi Hetairoi also known as the Army of the king which was created from absolute undying loyalty of his soldiers to follow him for all eternity.
Bellatrix Lestrange’s (Harry Potter) obsession of Lord Voldemort led her to become the most loyal of his Death Eaters. Bellatrix trained under the Dark Lord himself and was his best lieutenant.
Euclid (Highschool DxD) is extremely loyal to Satan Lucifer, the loyalty also extends to Lucifer's son Rizevim.
The Student Council (Highschool DxD) aka Sona Sitri's Peerage is loyal to their King to point where each of them follow all her orders without question…
…Genshirou Saji possibly the most loyal among her peerage is willing to surrender his own life and fight far stronger opponents to make her dreams a reality.
Occult Research Club (Highschool DxD) aka Rias Gremory's Peerage is composed of members all saved by their King causing them to be immensely loyal towards Rias…
…the most loyal is Issei Hyoudou, an individual willing to fight for his King to bitter end and has proven numbers of times during many life-and-death situations.
Peta (Marchen Awakens Romance) has known Phantom the majority of his life and is his most loyal soldier. He even accepted the Zombie Tattoo to stay with his captain for eternity and shares his ideals of the world. Peta is the only one Phantom considers a friend.
Kisame Hoshigaki (Naruto) loyally believes in protecting info, going as far as to slay comrades, his master, and even himself to achieve it.
Itachi Uchiha (Naruto) inadvertently trapped himself in Kotoamatsukami, which forces its target to follow the caster's orders and neutralizes all other forms of control, compelling him to protect Konoha and freeing him from Kabuto's Summoning Jutsu: Reanimation/Edo Tensei.
Roronoa Zoro’s (One Piece) allegiance to Luffy goes as far as to gamble his own life and dream to save his captain’s.
Enkidu's (TYPE-MOON) loyalty to Gilgamesh is so legendary and undying that even after being tormented by and being struck down by the gods, his loyalty didn't waver in the slightest.
The Hi Shin Unit (Kingdom) possess absolute faith and unwavering loyalty towards their captain and leader, Shin...
...that they're willling to use their themselves as shields.
Gyou' Un (Kingdom) posses such unwavering loyality to Rin Shou Jo of Three Great Heavens of Zhao, that he promised on his deathbed that he wouldn't follow his master into death.
Percy Jackson's (Percy Jackson and the Olympians) fatal flaw is loyalty. Athena said he would sacrifice the world to save a friend, she also said that the most dangerous fatal flaws are good in moderation. Hera correctly believed that Percy's loyalty to his friends would keep them together and allow them to complete the Prophecy of Seven.
Enya/Enyaba/N-Yah Gail the Hag (JoJo's Bizarre Adventure Part III Stardust Crusaders)
Gardevoir (Pokémon) is an exceptionally loyal Pokémon, willing to sacrifice its life for its trainer without hesitation. It's Mega Form is even empowered by the love it has for its trainer.