You can send 1 "Black Luster Soldier" monster from your hand to the Graveyard; until your opponent's next End Phase, this card's ATK becomes 3000, and this card's name becomes "Black Luster Soldier". You can banish this card from your Graveyard; add 1 "Beginning Knight" or "Evening Twilight Knight" from your Deck to your hand. You can only use each effect of "Super Soldier Soul" once per turn.
Black Luster Soldier cards and support focus on Ritual Summon plays. Banish Super Soldier Soul and add either Beginning Knight or Evening Twilight Knight to your hand. Then use Super Soldier Synthesis to summon Black Luster Soldier using the monster you searched and another monster from your deck as material.
You can use Super Soldier Soul paired with any Gaia monster as ritual tribute to make Black Luster Soldier. This also gets Super Soldier Soul in your graveyard to set up for a search.