来夏 is read as らいか (raika) and means next summer.
らいか
raika
らいしゅん
next spring
らいしゅう
next week
らいじょう
attendance
らいせ
afterlife
らいてん
coming to a store (restaurant, bar, shop, etc.)
らいかい
きかた
the way (to somewhere)
きて
someone who is coming
きしかた
the past
きたて
new arrival
らいきょう
coming to a capital city (esp. Tokyo or Kyoto)
らいねんど
next year