Beryl's Warhammer is magical, but currently only equivalent to a normal warhammer. If would like to have it....morph....as he levels up a bit if possible. Instead of him getting a magical item randomly or something, the item gets stored (not physically in the game world, but basically in the DM's piggy bank) and the bonus is applied when Beryl levels up.
If most characters will have a +1 level by level 4 for instance, when Beryl increases in level to 4, there is a special flash of light and the Warhammer alters slightly, becoming a Warhammer +1. Other changes can happen as well, elemental damage bonuses, larger size then normal (you do versatile damage 1d10 with one hand..or basically a +1 damage modifier..but for theme it would just be that the warhammer grows to fit Beryl's larger size and strength perfectly).
That actually is not very in tune with the spirit of D&D and something you really need to discuss with your DM if you want anything like it. Funny thing is, I did offer something like that to my party, involving a ring that came with a direct contract to a specific god, but they all said no.
Gifts to specific party members are extremely difficult to do well, especially when mechanically they would be just as useful to others. ---
Official Teetotaller of PotD Dovie'andi se tovya sagain!