Primitive Boyfriend Vol. 1 by Yoshineko Kitafuku
A girl is sent back in time to meet the man of her dreams--but he's a caveman?!
Seventeen-year-old Kamigome Mito yearns for romance, but the boys in her school all share the same flaw--they're hopeless wimps! When Mito prays for divine intervention, Spica, goddess of the harvest, sends her back in time to find a soulmate. The destination? Planet Earth, 2.5 million years ago!