Botsuraku Yotei no Kizoku dakedo, Hima Datta kara Mahou wo Kiwametemita / 没落予定の貴族だけど、暇だったから魔法を極めてみた

What's a guy to do when his life suddenly changes while innocently enjoying a nice, cold drink after work? And I mean really changes. This middle-aged commoner now finds himself in the body of Liam Hamilton, the young son of a noble house teetering on the brink of collapse. Between his fervidly desperate father and his utterly apathetic brothers, the only bright side to his new situation is that Liam can finally try learning magic like he's always wanted. Little does he know his hobby of choice may be about to turn his life upside-down yet again! Will Liam be able to master the craft of magic? And will it be enough to save him from the shadow looming over his family...? (Source: J-Novel Club)...