Shu and Valt have unspoken feelings for each other. Neither of them intend on telling the other about their feelings. However this doesn't mean they won't give the other hints about those feelings.
After an attack in the WBBA Valt and Shu make a promise to never leave the other's side until they find their attacker. Because of this promise the two slowly begin to find out their feelings towards the other. This causes confusion for them both but they still manage to get through each day. Whoever their attacker is...