Bulgarian sekiwake Kotooshu has obtained Japanese nationality, it was learned on Thursday.

The 30-year-old Kotooshu, whose real name is Kaloyan Mahlyanov, is the first European wrestler to become a naturalized Japanese. As a result, he has cleared the first hurdle toward becoming a sumo elder after he ends his career as a wrestler.

He is expected to take his wife's maiden name Ando.

Under Japan Sumo Association rules, wrestlers can only become sumo elders if they are Japanese nationals. Sumo elder membership, however, can only be obtained by purchasing toshiyori kabu, or elder stock, in the JSA.

There are only 105 shares available for purchase, and the increasing lifespan of elders has meant that they take longer to become vacant. As a result, their decreasing availability has caused their price to greatly increase, with stock now reportedly selling for up to ¥500 million.

Kotooshu made his sumo debut in 2002 and became the first European to reach ozeki in 2006.

However, his form has dipped in recent years due to injuries and he is currently wrestling at sumo's third-highest rank of sekiwake, having been demoted after pulling out on the fourth day of the Kyushu Grand Sumo Tournament in November with a dislocated left shoulder.

Kotooshu can regain his ozeki rank if he posts 10 wins at the ongoing New Year Basho. He has a 4-1 record after Thursday's win over Toyonoshima.