This is chapter 4 of the Sasuke Retsuden manga.
Summary[]
Sasuke visits the Astronomy Research Institute's library and seeks out Penjira, the library's attendant. Penjira is surprised when he sees Sasuke and shows him the book he's been looking at: it's about extinct dragons whose fossils can be found in the area near the Institute. Sasuke asks about the astronomy book that's supposed to lead to the polar particles' location. Penjira refers Sasuke to the library's book catalogue, which says that the book is stored in the basement. Penjira informs Sasuke that prisoners are forbidden from reading the books in the basement because they're too valuable, and anyone caught breaking that rule would be executed; he suggests trying a different book.
Sakura approaches them, claiming to have overheard and to now be curious about the astronomy book. Penjira is unwilling to make an exception for her, as he would be the one to be executed if she were caught. When Sakura suggests that they gamble for the key, Penjira reconsiders, but makes Sakura promise that, if she wins, she'll give the key back as soon as she's done. Penjira selects Hoshinarabe for them to play, a card game similar to poker. Sasuke offers to place a genjutsu on Penjira, but Sakura refuses. After she studies the cards and the rules, Sakura and Penjira start playing. The first game ends in a tie, with both of them ending up with the same hand. Penjira accuses Sakura of cheating, but since he has no proof they play another game. The next game is also a tie, as is the next and the next, until Penjira finally loses interest and turns over the key.
That night, Sasuke meets Sakura in the library. She asks if he's made sure that Jiji was asleep this time so that he won't interrupt them again. Sasuke reports that he made sure and, remembering Jiji's warnings about someone hitting on Sakura while he's away, creates a ring around her finger. Sakura makes no comment about the ring, but admires it distractedly. Sasuke regains her focus by asking how she cheated against Penjira. Sakura explains that, because of the cards' age, she was able to identify which card was which by the minor forms of damage to each of them. Although she could have used this information to win, she discovered from her time with Tsunade that tying is the most time-efficient way of defeating people with gambling addictions.
Before entering the basement, Sakura uses her chakra to sense the area ahead. In doing so, she notices that there's a secret basement accessible from Zansūru's office. They set this information aside and begin looking for the astronomy book. When they find it, they discover that the book contains the same pictures as appear on the Hoshinarabe cards, apparently the work of the Sage of Six Paths. Sakura speculates that the pictures may represent certain constellations, with each constellation meant to represent a particular month. She'll need to do some research in order to figure out which picture correlates to which month, but believes she can finish in two days. Sasuke leaves her to it, but, looking at the pictures again, can't shake the feeling that they are familiar somehow.