An option to buy is included in the deal, according to Sky Germany, with his medical scheduled for Thursday.
The move is a direct response to the injury sustained by new signing Yukhym Konoplya, who suffered a knee ligament tear against Rot-Weiss Essen and is set to miss the start of the season; Konoplya had arrived at Gladbach as a free transfer from Shakhtar Donetsk earlier this month and had been earmarked for the right-back role. Hashioka offers versatility as cover, capable of playing either at right-back or in central defence.
The Japan international has taken a winding route through European football since leaving boyhood club Urawa Red Diamonds, moving to Belgium's Sint-Truiden in 2021, then to Luton Town in January 2024, where he became the club's first-ever Japanese player and made 28 appearances including 10 in the Premier League.
He joined Slavia Prague, where his contract runs until 2029, last summer, and spent the second half of last season on loan at Belgian side Gent. He has won 12 caps for Japan without scoring, making his debut at the 2019 East Asian Championship and featuring at the Tokyo Olympics in 2021, though he was not selected for Japan's 2026 World Cup squad.
Hashioka becomes Gladbach's eighth signing of the summer under sporting director Rouven Schröder and will link up with fellow Japanese internationals Zento Uno and Shuto Machino in the squad. He could be available for Saturday's friendly against Hansa Rostock if his transfer is completed in time.
The loan adds further depth to a Borussia Monchengladbach squad that already includes Joe Scally and Kevin Diks as alternative options at right-back, with Scally also capable of playing on the left and Diks primarily viewed as a centre-back.
Schröder has previously said he wants to trim the first-team squad to around 25 players this summer, with several higher earners, including Jan Olschowsky, Tomáš Čvančara, Machino, Florian Neuhaus and Kevin Stöger, regarded as possible departures to help balance the books even as new faces continue to arrive.