After all, he still had a lot of Rejuvenating Pills. Furthermore, this pill was already of little use to him, but it would have a great effect on Yahiko.
He was not a skilled fighter, and he was not very old either. If Charlie simply scraped about one-tenth of the pill and dissolved it into a glass of water for Yahiko, the latter would surely be able to restore his health relatively quickly.
The reason why Charlie was not giving him the pill right now was mainly because Charlie wanted to take