Soul Eater. Vol. 4

This volume starts off with an immortal Wolf-Man with a demon eye being broken out of the witch jail by Medusa. It is the start of an experiment to test Maka and Soul. Meanwhile, Maka asks Dr. Stein for special training so she can become strong. He agrees, but tells her it is very dangerous - She and Soul could end up never being able to get their soul wavelengths to match up ever again. Maka decides to do it anyway. She and Soul argue over it. Maka wins out, and they go to London (along with Black Star and Tsubaki) for the assignment. There she fights the Wolf-Man, and the worst happens - She and Soul lose their compatibility. Maka can't even hold Soul any more. But through sheer determination, she and Soul manage to resonate again. Medusa watches the whole thing, observing the effect of the 'black blood' in Soul and Maka.