Abroad -> Sendai International Airport
If you come from abroad and land on one of the airports in Japan then take a connecting flight to Sendai International Airport.
Alternatively, it is possible to take a connecting flight from either Seoul or Taipei to the Sendai International Airport.
Airports -> JR Sendai Station
There is a direct train connection from Sendai International Airport to JR Sendai Station. To see the detailed schedule of Sendai Access Line between Sendai Airport and JR Sendai Station please go to the page: https://www.egakkai.com/ispac2019/info/transportation/
If you land at the Haneda airport, you could take trains from Haneda to Sendai by the high-speed train, Shinkansen, the "bullet train".
From Tokyo station to JR Sendai station, it takes about 1.5 hours (with Shinkansen) and one needs additional 1 hour from Haneda to Tokyo station