Financial details were not disclosed but British media reports said Europa League champions Tottenham paid a fee of five million pounds ($6.82 million) for the 20-year-old.
Takai, a product of Frontale's youth academy, was part of the side that missed out on the Asian Champions League Elite title after suffering a 2-0 defeat to Saudi Arabia's Al Ahli in the final in May.
He has also made four appearances for Japan's national team.
Takai is the third centre-back to join the North London club this summer, further bolstering their defence after the arrivals of Luka Vuskovic from Hajduk Split and Kevin Danso, whose loan move from RC Lens was made permanent.
Tottenham ended their 17-year trophy drought with their Europa League victory last season, but also endured their worst domestic campaign for nearly half a century and finished 17th in the Premier League.