In search of a reference book for a mortal blow, Hayate, Nagi and Maria visit the Sanzenin library. Hayate says that the place is huge, with Maria saying that it's a pain to clean this place. Hayate guesses that Nagi's personal shelf is the one with all the manga carelessly piled up, but Nagi says that she doesn't just read manga. Hayate also finds video game guides as well. He wonders if the book he is looking for is in the library or not. Maria then finds a book on how to perform mortal blows and gives it to Hayate, telling him that this book belonged to Himegami; the former Sanzenin butler. Nagi and Hayate start the training for a mortal but she trips and falls blaming the shoes for it. She asks Hayate to call her master with Maria thinking that she is a bad master. They go outside to practice. Nagi begins to read the examples, with the first one being set on fire but Hayate wants something simple to start with. As she was reading she comes across a page that said 'secret attack that will make the person you like love you more', causing Nagi to shut the book deciding that she wants to learn it. Hayate wants to borrow the book but Nagi denies his request and runs away with it. She looks in the book in learn about the secret move but finds out that it says to get naked. Nagi shouts at the book saying that she could never do something so embarrassing. Hayate yells at her to stop because she's heading to the edge of a cliff. Nagi falls of the edge but Hayate manages to use himself to brace her fall. After getting back to the mansion Hayate declares that he'll be able to learn a mortal blow to show Hinagiku. Nagi gets angry at this and burns the book before hitting Hayate on the head. Hayate goes to Maria asking her if she could teach him a mortal blow to make Nagi feel better, but she tells him that it will be difficult to learn one like that.
While at looking at Nagi's book shelves at the Sanzenin family archives, covers for various Shounen Sunday magazines can be seen.
After finding the Sanzenin secret attack handbook, Nagi asks Hayate to refer to her as "The undefeated of the north, south, east, west and central". This is a reference from the series Mobile Fighter G Gundam.
As Nagi reads an attack from the handbook to Hayate that involves being engulfed by fire Makoto Shishio from Rurouni Kenshin can be seen in her example.