Tsuna's father, who supposedly works at oil fields, rarely sees his family. Iemitsu is the great-great grandson of the first Vongola boss. Tsuna believes him to be a loser father who has nothing to do with the Mafia, but Iemitsu is actually a crucial member of the Mafia. Though not officially part of the Vongola Family, he is the "Outside Advisor", which is the second highest position, second only to the boss, when family crises arise. After Vongola IX chose Xanxus as his successor, Iemitsu, who wants Tsuna to become the next boss, protested. He traveled around the world while he waited for the 9th's reply.
He returned to Japan with Dino and brought with him the real halves of the Vongola Rings. Since he did not want anyone to know he was bringing the real halves, he instructed Basil, his subordinate and disciple, to bring the fake halves to Tsuna (though Basil did not know they were fake), in order to use him as a decoy. Even though he used him as a decoy, both Reborn and Dino believed that it was the right decision. Still, Basil remained loyal to him.
During Tsuna and his family's training, Iemitsu secretly watched over each one of them. During the battle for the Vongola rings, Iemitsu believed that the IX was dead. He went to Italy with his subordinates to verify his suspicions. When he supposedly found the IX, it was revealed that it was a fake IX.
In the Future arc, Iemitsu and his wife is currently on vacation in Italy.
Iemitsu usually carries a pickaxe around. He was also once known as the Vongola's "Young Lion". Source - Wikipedia
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