Giant Lord

The last item you require to unlock the final boss is the Giant's Kinship. The item is dropped by the Giant Lord upon defeat. Three strong enemies guard the gate to the arena of the Giant Lord. The video below shows how to skip the enemies:

Dark Souls 2: How to skip the Forest of Fallen Giants

The skip can be difficult to pull off. Have patience, and try and try again. Alternatively, reach the gate as the game intended.

Forest of Fallen Giants

Speedrun to The Place Unbeknownst bonfire NG+7, Dark Souls 2 SotFS

Start from the Cardinal Tower bonfire and climb down the nearby ladder. Dispatch of the Hollow Infantry x 2 and the Hollow Soldier near the bridge. Use the Soldier Key to open the door, proceed ahead, turn left, and you should find two red phantoms. A Royal Guard is standing to your right. Defeat the red phantoms first, then the Royal Guard. If the two red phantoms run after you, use the various narrow passageways to funnel the enemies and spam Crystal Soul Spear at them. The spell would usually hit both enemies if the red phantoms are aligned in one file. Equip the King's Ring to open the iron gate, enter, and light The Place Unbeknownst bonfire. Attune any spells you need for the upcoming boss fight. Dark Weapon is especially effective against the Giant Lord. Interact with the giant tree and be transported to the Memory of Jeigh.

Giant Lord

Red Iron Twinblade versus Giant Lord NG+7, Dark Souls 2 SotFS

This boss is weak against dark. Buff your weapon with Dark Weapon; the Red Iron Twinblade+10 is recommended. Equip the Dark Clutch Ring to boost your dark damage output. Furthermore, ensure you have the Blue Dagger as an offhand weapon while you two-hand the Red Iron Twinblade. You want to hit one of the boss' legs a few times, then switch to the other leg. Rinse and repeat. The best window to punish is when the boss does a swipe of his sword as if he is swinging it downward like a U. To bait this attack, stand behind the boss and between his legs. When the boss is about to do the U-attack, move forward a bit between the boss' legs so your character is in front of the boss. Get in a few hits.

Defeat the Giant Lord, head downstairs, and interact with the giant corpse to receive a Soul of a Giant. Interact with the corpse again to be transported back to the Forest of Fallen Giants.