Jones said versatility had "100%" played a part in his selection choices after surprisingly going with 33-year-old winger Toshiaki Hirose and flyhalf Kosei Ono for tournament.
"We know Kosei can fill in at nine, while Hirose has special qualities as he can play 10 and wing and his leadership off the field is so important for us," Jones was quoted as saying by Kyodo News on Monday.
Jones went for a split of 17 forwards and 14 backs in the squad skippered by Chiefs backrow forward Michael Leitch.
Clubless No 8 Hayden Hopgood was one of eight players trimmed from Jones's training squad. Jones had sympathy for the New Zealand-born backrow forward.
"Foreign players in Japan get criticised a lot, but Hayden spent the last five months without any pay trying to get into the squad even after his wife had a baby," said Jones, who will step down after the tournament in England.
"One of the most unpleasant things in coaching is telling players they are not in the squad."
The Brave Blossoms will depart for England on Tuesday (local time) where they have been drawn in Group B alongside Scotland, Samoa, South Africa and the United States.
Japan are looking for only their second World Cup win following their 1991 success over Zimbabwe.
They face Georgia in a final warm-up in Gloucester on Saturday.
Squad:
Keita Inagaki, Masataka Mikami, Kensuke Hatakeyama, Hiroshi Yamashita, Shota Horie, Takeshi Kizu, Hiroki Yuhara, Luke Thompson, Shinya Makabe, Shoji Ito, Hitoshi Ono, Michael Leitch (captain), Ryu Holani, Michael Broadhurst, Hendrik Tui, Amanaki Lelei Mafi, Justin Ives, Fumiaki Tanaka, Atsushi Hiwasa, Harumichi Tatekawa, Yu Tamura, Kosei Ono, Craig Wing, Male Sa'u, Kenki Fukuoka, Akihito Yamada, Karne Hesketh, Yoshikazu Fujita, Ayumu Goromaru, Kotaro Matsushima, Toshiaki Hirose.
