Theron whips out big guns
Captain and centre Jeremy Ward will partner with JT Jackson in the midfield. Jackson is one of two survivors of the 2015 edition of the tournament in Italy.
The loose trio that featured in all three of the team's warm-up matches in South Africa - flanks Zain Davids and Ernst van Rhyn, as well as No.8 Junior Pokomela - has been retained for the match.
Flyhalf Manie Libbok and Kings scrumhalf James Hall will form an exciting halfback combination.
The team also includes a talented back three of wings Mosolwa Mafuma and Sibusiso Nkosi, as well as fullback Curwin Bosch.
In the front row props Kwenzo Blose and Jaco Holtzhausen will pair up with hooker Tango Balekile.
"We selected a strong team to lay the foundation for our campaign against a highly-motivated Japan side," said Theron.
"These players all proved their worth in the warm-up matches as individuals and as combinations, and we are excited by what they can do if they play to their potential.
"The players have settled in well since we arrived in Manchester and I have been pleased with the quality of our training sessions and the players' attitude, and hopefully they will transfer that onto the field on Tuesday."
Theron said the weather was surprisingly pleasant in Manchester, and he said if it continued through to Tuesday, it could assist them.
"The weather has been amazing since Friday," said the coach.
"The sun has been shining and it has been very warm. On Sunday the players were scrambling for sunblock at training and we have had to have short sharp training sessions to prevent them from being in the sun too long.
"This is a real bonus because it is weather conditions we are used to; we have been training in this weather since the squad assembled early in April."
Looking ahead at the clash against Japan, Theron expected them to spread the ball wide and test the Junior Boks' defence.
"We expect Japan to be motivated, competitive and they will try to run at us," said Theron.
"They will also put a lot of effort into the set pieces, so we are anticipating a tough challenge all around."
South Africa Under-20: 15 Curwin Bosch, 14 Sibusiso Nkosi, 13 Jeremy Ward (captain), 12 JT Jackson, 11 Mosolwa Mafuma, 10 Manie Libbok, 9 James Hall, 8 Junior Pokomela, 7 Ernst van Rhyn, 6 Zain Davids, 5 Eli Snyman, 4 Cobus Wiese, 3 Jaco Holtzhausen, 2 Tango Balekile, 1 Kwenzo Blose.
Replacements: 16 Franco van den Berg, 17 Jan-Henning Campher, 18 Carlü Sadie, 19 Ruben de Villiers, 20 Denzel Hill, 21 Embrose Papier, 22 Franco Naude, 23 Keanu Vers.
Date: Tuesday, June 7
Venue: Academy Stadium, Manchester
Kick-off: 15.15 (16.15 SA time; 14.15 GMT; 23.15 Japan time)
Referee: Elia Rizzo (Italy)
Assistant referees: Craig Evans (Wales), John Meredith (England)
TMO: John Mason (Wales)