Before going freelance, he was working for the Crossbell News Service.
Apart from his keen perception, Nielsen is armed with an extensive network of connections, including the fellow journalist editor-in-chief of the Liberl News, inspector Guy Bannings of the Crossbell Police Department, librarian Miles Neues from Crossbell's public library and elder Quint, the grave keeper of the Crossbell Cathedral.
There are many enigmas revolving around Nielsen. For example, on the day of Guy Bannings' death, he thought it was a good idea to exchange information and they agreed to meet at the jazz bar Garante. This strengthened his interest in solving the mystery around Guy's death and this perseverance lead to traces to bracer Arios MacLaine and lawyer Ian Grimwood.
His perceptiveness and knowledge ultimately led to fueling suspicions that he might be affiliated with Ouroboros.
- After his news coverage on the Stargazers' Tower in Crossbell, the enormous book collection disappeared from the tower's library.
- His timing is suspicious. He returned to Crossbell on the day of Guy Banning's death in S.1201 and once again in the latter half of S.1204 when the Phantasmal Blaze Plan was set in motion. Guy was considered a hindrance for the completion of the Phantasmal Blaze plan. When Crossbell was under pressure of suzerains Erebonia and Calvard, he did not return to Crossbell while this would have had a significant amount of value for a journalist.
- If both Guy's parents and Ian's relatives were onboard of the aircraft that crashed, and Ian would have devised the Azure-Zero Project out of personal grudge toward Erebonia and Calvard, then that would have been a weak motive to murder Guy.
- Similarly, he understands the suffering over Arios MacLaine over the passing of his wife Saya MacLaine and his blinded daughter Shizuku MacLaine, providing him with a motive to join the Azure-Zero Plan without a way to back out.
- With barely any foundation, he readily guessed the fact that KeA was born during the Middle Ages.
- While Nielsen was reporting the Hundred Days War, Leonhardt and Joshua Astray joined Ouroboros while the imprisoned Bleublanc escaped from and also joined Ouroboros.
- During his stay in Crossbell, Mariabell Crois and Shirley Orlando were scouted by Ouroboros.
- If he is indeed affiliated with the upper echelons of Ouroboros, he provided the Special Support Section with numerous hints under the pretense of reporting, such as the "ancient oath" of the Holy Beasts and the "treasure" being the "child" giving an "answer" before it.