I think you'd better do it in two days, as doing it in 1 day looks pretty impossible. The fox village is a 1 hour drive away from Sendai, so you can probably do some other sightseeing too on the day you go there. http://sendai-travel.jp/activities/zao-fox-village/
But for Tashiro island, first you need to get to the harbor in Ishinomaki, about 1.5 hours from Sendai, and then get on a ferry for a little less than an hour. There are only 3 ferries per day and you’ll need to take the 9am or the 13pm to actually have time to sightsee and be able to get on the last 15:30pm one back to Ishinomaki. So this is an all day thing. http://sendai-travel.jp/activities/tashiro-island/