Two on debut as Sunwolves change it up
Lemalu will start at lock, where he will partner Hitoshi Ono - while regular lock Liaki Moli moves to the flank and Yoshiya Hosoda drops down to the replacement bench.
Stewart's inclusion on the left wing is one of three changes to the backline.
He replaces Mifiposeti Paea, who also drops down to the bench.
Akihito Yamada returns on the right wing, with Viliami Lolohea dropping out of the matchday 23 all together.
The Sunwolves sit second from last in the Africa conference, just above the Southern Kings - with sevens points and one win from their eight matches.
The Force are last on the Australasian conference, with six points and one win in nine outings.
The two teams have never met in Super Rugby before.
Sunwolves: 15 Riaan Viljoen, 14 Akihito Yamada, 13 Derek Carpenter, 12 Harumichi Tatekawa, 11 John Stewart, 10 Tusi Pisi, 9 Kaito Shigeno, 8 Ed Quirk, 7 Andrew Durutalo, 6 Liaki Moli, 5 Faatiga Lemalu, 4 Hitoshi Ono, 3 Shinnosuke Kakinaga, 2, Shota Horie (captain), 1 Masataka Mikami.
Replacements: 16 Takeshi Kizu, 17 Ziun Gu, 18 Takuma Asahara, 19 Yoshiya Hosoda, 20 Taiyo Ando, 21 Atsushi Hiwasa, 22 Yu Tamura, 23 Mifiposeti Paea.
Date: Saturday, May 7
Venue: Prince Chichibu Memorial Stadium, Tokyo
Kick-off: 14.15 (13.15 AWST; 05.15 GMT)
Referee: Mike Fraser
Assistant referees: Paul Williams, Aki Aso
TMO: Takashi Hareda