Spurs are looking to revive their fortunes in the Women's Super League with the team in eighth place on nine points after 10 games, 16 points adrift of Arsenal who are third.
Defender Iwabuchi, who won the World Cup in 2011 with Japan, has made only three appearances for Arsenal this season and has joined Tottenham in search of more playing time ahead of the Women's World Cup later this year in Australia and New Zealand.
Iwabuchi moved to England in 2020, spending half a season with Aston Villa before signing for Arsenal, where she scored on her debut in the Women's Champions League.
"I'm an intelligent player," Iwabuchi, who has scored 37 goals in 85 games for Japan, said.
"I bring that on the pitch for the team and try to contribute."
Iwabuchi is Spurs' second signing of the January transfer window after they brought in England forward Bethany England (28) from Chelsea in a British record deal.