Rurouni Kenshin OVA: Reflection (Seiso-hen)

Taking place after the series has ended, it is mostly told in the point of view of Kamiya Kaoru. After their marriage Kenshin continues to wander, sick with an unknown disease. Kaoru, wanting to share the pain with Kenshin, asks Kenshin to infect her with the disease as well. However, because of Kenshin's prolonged absence, his son Kenji, becomes a troubled teenager that seeks out Hiko in order to become an even better swordsman than his father ever was.

Synopsis from Anime News Network