Leitch returns to the back row after starting on the bench in their surprise win over Ireland, although Pieter Labuschagne retains the captaincy.
Atsushi Sakate starts at hooker and Wimpie van der Walt comes in at lock as coach Jamie Joseph makes three changes.
Shota Horie drops to the bench despite being man of the match against Ireland.
Fiji power past GeorgiaFrance make 11 changes for Tonga matchEtzebeth accused of racial abuse
The Brave Blossoms, who top Pool A, are targeting a first World Cup quarter-final after falling in the group stage four years ago, despite winning three matches.
Victory over Samoa at the City of Toyota Stadium would put them in a strong position to reach the last eight before facing Scotland in their final Pool A game.
Meanwhile, Samoa have made six changes to the side that failed to score a point in their defeat by Scotland.
Loose-head prop Jordan Lay, second-row Piula Faasalele and fly-half Ulupano Seuteni all make their first starts at the tournament, as does hooker Seilala Lam, who is the brother of captain and number eight Jack.
Teams
Japan: Nakayama; Matsushima, Lafaele, Nakamura, Lemeki; Tamura, Nagare; Inagaki, Sakate, Ji-won, Van der Walt, Moore, Leitch, Labuschagne, Himeno
Replacements: Horie, Nakajima, Ai Valu, Helu, Tui, Tanaka, Matsuda, Fukuoka
Samoa: Nanai-Williams; Tuala, Leiua, Taefu, Fidow; Seuteni, Polataivao; Lay, S Lam, Alaalatoa, Faasalel, Le’aupepe, Vui, Ioane, J Lam
Replacements: Niuia, Alo-Emile, Lay, Toleafoa, Tyrell, Cowley, Pisi, Fonotia