When Bruce Banner was hired for the Gamma Bomb Project, he discovered that General Ross and most of the people involved in the project were not convinced it would ever succeed. But Hank, a technician, did believe in the project and viewed Dr. Banner as a friend. He befriended the lonely genius and introduced him to his wife, Lois. Lois was pregnant and soon gave birth to Po. The couple ask Bruce to be her godfather. He had no idea what that meant and stayed silent. They took his silence as a "yes".
With Po as a baby, there was little interaction between her and "Uncle Bruce". He would wave to her before picking up her father for work. But the Gamma project took several years to complete and Po was growing up. Lois was often preoccupied and Hank would take their daughter to work. There she started really interacting with Uncle Bruce, deciding he was "the coolest person on Earth". Po became Bruce's greatest fan.
Po was precocious, starting to ask endless questions about science. Most were simple and Bruce could answer them easily. Some were not. She asked Bruce questions concerning the lab rats, test subjects used for radiation experiments. She asked why did the rats had to "go bye-bye". He gave her an answer about the greater good. She countered with a question about sadness and tears caused by their "bye-bye". While Bruce refused to acknowledge the deaths caused by his project, Po became obsessed with death. She also developed a "morbid curiosity" concerning the afterlife. Po believed she could communicate with dead things. Whether it was dead squirrels, dead birds or old skulls, Po would speak to them. And they supposedly answered back, whispering secrets, telling the truth. Her dad thought her obsession was creepy.
By the time Po was 7-years-old, Hank had apparently left the Gamma project. He had a business of his own, dusting crops and taking tourists on rides in an old biplane. Bruce was still hanging out with them and helping a little bit with their business. He even sung a lullaby to Po. It was rather morbid but became her favorite. One day, Hank decided to take Po with him on a flight. She would fly with him on the pilot's seat. Bruce modified the seat to have two safety harnesses. He lectured her about their use in case of emergency and about the importance of the controls. Particularly that she should not touch them while on flight. Hank and Po took off on their old biplane. They never returned. Bruce mourned them, but a few weeks later his own life took a turn for the worse. He was caught in the explosion of his own Gamma Bomb and turned into the Hulk.
In his first transformation, the Hulk trashed Banner's office. When Banner returned to clear the mess, he found a child's drawing on the floor. One of Po's drawings, this one depicting part of her first and only flight. A drawing apparently completed by a ghost. Over the following "twenty years", Bruce would lose many other people. To the point Bruce started feeling numb inside, becoming unemotional again. But then Po entered his life again.
During a period of heavy snow, Hulk went to sleep in the vicinity of Po's grave and Wolverine crash landed nearby. Po communicated with them both, enlisting them in a mission of rescuing her daddy ... and herself. During the mission, the duo pieced together what had happened to Po. In her final flight, the little girl had touched the controls and caused the biplane to crush. She sang her favorite lullaby during the fall. The biplane landed in the bottom of a lake. Po was killed instantly while Hank was drowning. Po's ghost materialized nearby, thinking she had somehow escaped and trying to summon help for her father. For two decades she alternatively agonized about rescuing him or wallowed in guilt about killing him. She recognized the Hulk as her Uncle Bruce but had trouble communicating with him. She found Wolverine had no trouble seeing or speaking to her, making her wonder if he was somehow dead. He led them in recovering the remains of the biplane and its two passengers, beneath a lake dried up for years. Then she was left to rest in peace. Wolverine was happy about rescuing a little girl from agony, Hulk was left shedding a tear for his goddaughter.
Powers and Abilities
Po demonstrated a number of ghostly powers. She could apparently materialize at will to communicate, though her form was fluid between a rather realistic form and a childish drawing. Her materialized body could have the same functions as any other, such as sleeping, feeling hungry or urinating. She could move objects in this form, such as pushing Wolverine down a hole. She could also attack using her hands, fast enough to stun Wolverine. She could perform short-distance teleportations. Her singing caused pain to the Hulk, implied to be psychosomatic in nature.
She could briefly enter individuals for a variety of effects. In the Hulk, Po manipulated the fluids in his inner ear to cause him to loose balance and pass out. In Wolverine, she gave a small boost to his healing factor and scanned his overall health. She noted a pretty sick liver and suggested Wolvie has been drinking too much.