Hagino and Ikee were named among a team of 18 athletes Monday by the Japan Swimming Federation for the 23-30 July competition in Budapest.
Hagino, who ended 20 years of American supremacy in the men's 400 metres individual medley to win Olympic gold in Rio last year, will be a marked man despite still feeling his way back to full fitness after elbow surgery last September.
He faces a challenge from compatriot Daiya Seto, who will be looking to complete a world treble in the 400m individual medley in Hungary, having upset Hagino last week at the Japanese championships in Nagoya.
Hagino beat American Chase Kalisz into second with Seto taking bronze at the Rio Olympics and silver in the 200m behind Michael Phelps.
"I've never won a world title so I'll give everything I have," said Hagino, who hit back to beat Seto in the 200m IM at the weekend.
