The Anko & Mascarpone sub looks to be on about 3-inches of Subway bread and comes filled with red bean paste and mascarpone cheese for 170 yen (~$1.55 US). A version with only red bean paste is also available for 130 yen (~$1.18 US).
Mascarpone is regularly available on the Subway Japan menu while red bean paste is not.
Sweetened red bean and bread is a fairly common pairing in Japan as well as a number of other Asian countries.
Photo via Subway Japan.