According to the Official Rules set forth by the JPBPA, every team in the NPB is allowed to sign players to Ikusei contracts if they have more than 65 players on their rosters (Ikusei Rule 3).

Ikusei Requirements

• Players that have never signed contracts with NPB teams in the past are allowed to sign Ikusei contracts (Ikusei Rule 4.2).
• Players that were picked during the Secondary Draft are eligible for Ikusei contracts (Ikusei Rule 4.3).
• A player that has his contract cancelled and officially announced as such by the Commissioner can also be signed to Ikusei contracts (Ikusei Rule 4.8).

There are no set limits on the number of Ikusei players a team can carry. However, the Executive Committee may ask teams to adjust the number of Ikusei players on a team's roster if necessary (Ikusei Rule 5).

Up to 5 Ikusei players can be used during Ni-gun games (Ikusei Rule 8.2). When these players appear in games, they must wear 3-digit uniform numbers (Ikusei Rule 8.4).