Totosai and Tenseiga's Upgrade
Totosai appears before Sesshomaru and grants Tenseiga the ability called Meidou Zangetsuha. This technique allows Tenseiga to create pathways between the realms of life and death, a significant enhancement to its powers.
Inuyasha's Battle with Nikosen
During Inuyasha's new-moon human phase, the group faces the youkai Nikosen, who possesses the ability to survive decapitation. Inuyasha manages to absorb Nikosen's power into Tetsusaiga at sunrise, thus preventing any backfire from using the Dragon-Scaled Tetsusaiga.
Kanna and Mouryoumaru
Kanna escapes from Naraku's control and informs Moryomaru about Kinka and Ginka, two brothers who share the same youkai body. Their unique ability of shared blood would potentially strengthen Moryomaru's already formidable armored shell.