Yomei Hantoshi to Senkoku sareta node, Shinu Ki de "Hikari Mahou" wo Oboete Noroi wo Tokou to Omoimasu. Noroware Ouji no Yarinaoshi

Prince Callus was born with a mortal curse that marks him as a Taboo Being. His days are numbered, and he's been told the last six months of his life will be nothing but bedridden suffering. This grim future haunts him...until he meets Gourley, who can wield light magic. Callus becomes the magician's apprentice in hopes that this legendary power might dispel his curse if he can manage to master it in the time he has left. He has immense magical energy and the rare ability to see spirits on his side, after all, not to mention friends and family who are there to support him every step of the way. And so Callus stakes his life on this mission... It's time to learn light magic or die trying! (Source: J-Novel Club)