While financial specifics were not revealed, reports from British media indicated that the Europa League champions Tottenham paid a transfer fee of five million pounds ($6.82 million) for the 20-year-old.
Takai, who came through Frontale's youth academy, was part of the team that fell short of the Asian Champions League Elite title after a 2-0 loss to Saudi Arabia's Al Ahli in the final in May.
He has also represented Japan's national team four times.
Takai is the third center-back to join the North London club this summer, enhancing their defense following the additions of Luka Vuskovic from Hajduk Split and Kevin Danso, whose loan from RC Lens has been made permanent.
Tottenham ended a 17-year trophy drought with their Europa League win last season, but they also faced their worst domestic campaign in nearly fifty years, finishing 17th in the Premier League.