Complex sentence: Also, Knives further learns how to increase his power by merging with other plants, demonstrated on multiple occasions in the manga where he absorbs his "sisters" into his left arm, taking their power source into his.
Split into simpler sentences: Also, Knives further learns how to increase his power by merging with other plants. As is seen in multiple instances in the manga where he absorbs his "sisters" into his left arm, taking their power source into his.