Kikyo (InuYasha) must regularly absorb dead souls to sustain her undead body.
Tony Stark/Iron Man (Marvel Comics) depends on an arc reactor in his chest to prevent shrapnel lodged in his body from entering his heart and killing him.
Joshua (No Ordinary Family) requires special injections not only to retain his powers, but to stay alive.
Saya Otonashi (Blood+) requires regular blood transfusions to maintain her vitality.
Mr. Freeze (DC Comics) must be kept at sub-zero temperatures to survive.
Frank West (Dead Rising) requires the Zombrex drug to prevent from becoming a zombie himself.
Quarians (Mass Effect) are dependent on specialized environmental suits because of their near-nonexistent immune systems.
After being severely burned on Mustafar, Anakin Skywalker/Darth Vader (Star Wars) was placed into a mobile life support unit to sustain his life.
After losing his body's ability to regulate temperature, Python (Metal Gear Solid: Portable Ops) must wear a special cooling suit filled with liquid nitrogen or risk being literally burned alive from the inside out.
After losing his immune system, Mason Eckhart (Mutant X) must wear synthetic skin, a white wig, and gloves to avoid infection.
Abe Sapien (Hellboy/BPRD) must wear a special breathing apparatus when outside of water for prolonged periods.
Like Joshua, Dr. Dayton King (No Ordinary Family) needs the serum to keep himself alive as well as to resist the cancer he had 18 years ago.
Darien Fawkes (The Invisible Man) needs regular injections of a special counteragent or risk being driven insane by the Quicksilver in his system.
Due to a design flaw that renders her brain unable to produce enough serotonin, Max Guevara (Dark Angel) must ingest tryptophan or drink milk in order to avoid losing her powers and/or suffering violent seizures.
Albert Wesker (Resident Evil) needs to regularly inject himself with a specialized serum to keep the virus inside his body in check.
Drahmin (Mortal Kombat) needs to wear the Face of Kun-Lo to prevent himself from losing his mind to an oni's mindless rage.
Raziel (Legacy of Kain) must regularly consume souls to maintain his physical body or risk being shunted back to the Spectral Realm.
Invisible Woman (Marvel) needs to wear a special suit in order to be completely invisible which has no effect on normal clothes.
The Human Torch (Marvel) needs to wear a special suit that is completely immune to fire due to ordinary clothes would burned off.
Two-Face mostly relies on his coin to make his decisions.
Due in part to their severe psychological trauma, the members of the Beauty and the Beast Unit can only survive outside of their suits for a few minutes.
Like all vampires, Angel (Buffy the Vampire Slayer) must regularly ingest mammalian blood to maintain his vitality.
After suffering irreparable damage to his heart and lungs, Dingo Egret (Zone of the Enders) is forced to remain inside the Orbital Frame Jehuty to preserve his life.
After being severely burned by Kintaro, Kabal (Mortal Kombat) must now wear a breathing mask and mobile life support to remain alive.
As his new cyborg body lacks self-repair units of its own, Raiden (Metal Gear) must periodically steal fuel cells and batteries from other robots and cyborgs to recharge and heal.
Utsuro (Gintama) relies on the Altana of Earth for his immortality, and prolonged separation would cause his accumulated supply to run dry.
Kouka (Gintama) relies on the Altana of Kouan for her immortality, and prolonged separation caused her accumulated supply to run dry, which led to her death.
Hidan (Naruto) has to lick someones blood and stand in the Jashin symbol to complete his curse.
Toothless (How to Train Your Dragon) needs Hiccup to stabilize his new modified tail to fly.
Despite being immortal, Chase Young (Xiaolin Showdown) needs to drink the Lao Mang Lone Soup everyday to retain his human form and to stay young forever.
Kojō Akatsuki must taking some of his own blood to stop his vampiric urges take over when he gets aroused either through smells or other things.
Yume Hasegama must eat her brother's flesh to prevent from becoming a monster herself.
Due to his small body making incapable of flying, Arpeggio (Sly Cooper) build a mechanical birdcage on wheels to help him travel.
Glory (Buffy the Vampire Slayer) needs to periodically drain the sanity of others to maintain her own, but to also to keep Ben from gaining control.
Bui (YuYu Hakusho) wears a special type of armor to contain his demon energy which he lacks control over.
Mizore Shirayuki (Rosario + Vampire) must regularly keep a special lollipop in her mouth to maintain her body temperature outside of cold environments.
Sora and Shiro (No Game No Life) must reliance mutually and be closed together to fight opponents...
...If they're separated, this is terrific example, Shiro without Sora...
...another terrific example, Sora without Shiro.
As a unique zombie, Rea Sanka (Sankarea) must consume hydrangea leaves to remain lucid and too keep her body from decaying.
In order to use his Bio-Organic Thermokinetic Blasts, Black Tom Cassidy(Marvel) requires a wooden object to focus them through, such as his shillelagh.
If Android 10/Dr. Gero (Dragon Ball Z) and Android 19 are away from Dr. Gero's Lab, they need to absorb energy...
...or else they'll drain their power reserves and begin to malfunction.
Roger (American Dad!) and his alien species must constantly act mean and cruel to stay alive, as otherwise their "bitchiness" will turn to bile and poison them to death.