First of all, i would like to tell you who is the god Váli.
Vali, as it is told in the Skaldskaparmal, is the “son of Odin and Rind, stepson of Frigg, brother of the Æsir, Baldr’s avenging As, enemy of Hod and his slayer, father’s homestead-inhabiter.”
Váli is also among the twelve Æsir seated as judges at Ægir’s banquet. He is not only seen as a God of vengeance, but truly one of the Æsir, seated with the others at table and drink. He is referenced for his courage and his accuracy with the bow, and is one of the inheritors of Asgard after Ragnarok.
The Birth of Váli
The prophecy made by Rossthiof was duly fulfilled, for Rinda bore a son named Vali (Ali, Bous, or Beav), a personification of the lengthening days, who grew with such marvelous rapidity, that in the course of a single day he attained his full stature. Without even taking time to wash his face or comb his hair, this young God hastened off to Asgard with bow and arrow to avenge the death of Balder, God of light, by slaying his murderer, Hodur, the blind God of darkness.
Of course, metaphorically speaking, he hasn’t born just for a single purpose, to avenge the death of Baldr, and he did not took a single day to grow and run to Asgard to kill Hodr, this tale is told, for us to have that perception that Váli was quickly trained to become a great warrior, an archer, and he grew with such skills, that he became a great god, and too soon he proved his abilities, his skills.
Also, there is a tale which says that de God Hoder (the Danish version of the god Hod / Hodr) was the lover of Nanna the princess of the Danes. Balder also desired Nanna and tried to woo her without success. Undeterred Balder raised an army of gods and attacked Hod with a fleet of ships. Hoder successfully held them off and even managed to break Thor’s weapon ( apparently in this time, Thor did not owned his magic hammer Mjölnir ) Hoder eventually killed Balder using a magical sword. Odin’s son Bo ( Váli ) later avenged Balder.
Why is it Váli’s day at the same day as Valentine’s Day ?
Vali is the God of eternal light, just as a beam of light was often called with arrows, he is always represented and worshiped as an archer. For that reason his month in Scandinavian an now in Neopaganism of Northern Beliefs calendars is designated by the sign of the bow, and is called Lios-beri, the light-bringing. As it falls between the middle of January and of February, the early Christians dedicated this month to St. Valentine, who was also a skillful archer, and was said, like Vali, to be the harbinger of brighter days, the awakener of tender sentiments, and the patron of all lovers.