When Jack killed Evil Janus, he received exp points. At the same time, he also received a notification that his quest, The Attack on League Factions, was completed. He received 10,000,000 exp, 100 gold coins, and 10,000 mana cores.
This was an SSS-difficulty quest. Normally, there was an additional reward accompanying such a quest. A reward that might be legendary-grade items. He wondered if the technique book Janus gave him was that additional reward. However, he would expect a mega spell equivalent to a legendary-grade item to be eight-rune or nine-rune, not this seven-rune Storm Wrath. Even so, he didn't complain.
Probably the hidden reward was the blessing from the Healer Society so that he could build the wonder building, Revival Pool. Now that the murder case of the faction leaders had ended, he should be able to meet Panacea, the Healer Society's leader. He would arrange so once he returned to Thereath palace.