The Scarlet Letter allows Hawthorne to convert his own blood into holy words and control them, which he considers as the Word of God meant to aid him in administering punishment to the unjust. It can be used for offense through converting Hawthorne's blood into bullets of varying calibers and intensities. He can also form a shield using the ability to deflect an opponent's attack. Notably, the ability is quite similar to Ryunosuke Akutagawa's Rashomon, both of which manipulate matter at various ranges for both offensive and defensive usage.
The ability can work almost indefinitely from any source as long as Hawthorne's blood is intact. As such, it can be activated remotely even from inside a fountain pen with his blood inside it to launch a surprise attack to his opponent. However, it will not work when his blood gets diluted, specifically when it is drenched in water.
Aside from creating blood bullets for combat, Hawthorne can utilize his ability in various other ways, including pseudo-levitation. For instance, a pool of Hawthorne's blood can prove to be a source of his "steps" where he can walk on to make him appear that he can levitate or walk through air. This pool can also serve as a source of almost invisible blood bullets that are shot away from a target's point of view, which are quite elusive and unavoidable even for the likes of Yukichi Fukuzawa.
In addition, Hawthorne can create a thread made out of his blood using his ability. For example, he once tied a thin thread of blood and attached it onto Atsushi Nakajima while the latter and Lucy Maud Montgomery were transported to Anne's Chamber. Hence, because he was stealthily connected to Atsushi through the blood thread, Hawthorne also got transported into the dimension. However, because nothing can harm nor attack Anne inside the chamber, Hawthorne's blood bullets were ineffective against the giant doll.
The ability is a reference to The Scarlet Letter, a historical fiction novel by Nathaniel Hawthorne in 1850. It is about the story of Hester Prynne who conceives a daughter through an affair and then struggles to create a new life of repentance and dignity. The novel also has religious themes of legalism, sin, and guilt.
- In its most basic form, Hawthorne turns his blood into the letter "A". This is a reference to the original novel, in which the main character is required to wear a scarlet letter "A" on her dress at all times to shame her.
- The ability's reference work, The Scarlet Letter, is considered by various academics as a notable work representing the Great American Novel. Though the list of candidates for the merit is dynamic and relative, other candidates on the list include works of the real-life counterparts of the in-series Hawthorne's former co-members from the Guild, namely Moby-Dick by Herman Melville, Adventures of Huckleberry Finn by Mark Twain, The Great Gatsby by F. Scott Fitzgerald, and The Grapes of Wrath by John Steinbeck.
- Interestingly, these works are the exact names or references of the abilities of their corresponding users in the series.