The winning side of the line
Kachi-koshi means finishing a tournament with more wins than losses. A wrestler who competes on all 15 days reaches it with an eighth win. Seven wins is not enough, even if the record shown midway through the tournament is 7–1.
Wrestlers in the four lower divisions normally have seven scheduled bouts, so four wins gives them kachi-koshi. Absences and unusual schedules can make a final record look different, but the basic test remains a majority of wins.
A kachi-koshi usually leads to promotion on the next banzuke. The size of that move is not automatic. Rank, final score, open positions, and the records of surrounding wrestlers all affect where someone lands.