Sure, I'd be happy to help you plan your 4-day trip to Osaka! Here's an ideal itinerary for you:

Day 1:

• Start your day by visiting the iconic Osaka Castle. This historic castle is one of the most popular tourist attractions in Osaka and offers stunning views of the city.
• After exploring the castle, head to Dotonbori, a lively street filled with shops, restaurants, and entertainment. Try some local street food and take in the vibrant atmosphere.
• In the evening, visit the Umeda Sky Building for panoramic views of the city at night.

Day 2:

• Begin your day by visiting the Shitennoji Temple, one of the oldest temples in Japan. This temple is known for its beautiful architecture and serene atmosphere.
• Next, head to the Kuromon Ichiba Market, a bustling market filled with fresh seafood, fruits, and vegetables. Try some local delicacies and shop for souvenirs.
• In the afternoon, visit the Osaka Aquarium Kaiyukan, one of the largest aquariums in the world. See a variety of marine life, including whale sharks and dolphins.

Day 3:

• Start your day by visiting the Sumiyoshi Taisha Shrine, a beautiful shrine dedicated to the gods of the sea and travel. Take a stroll through the peaceful grounds and admire the traditional architecture.
• Next, head to the Shinsekai district, a vibrant neighborhood known for its retro charm and delicious food. Try some local specialties like kushikatsu (deep-fried skewers) and takoyaki (octopus balls).
• In the evening, visit the Abeno Harukas building for stunning views of the city at sunset.

Day 4:

• Begin your day by visiting the Osaka Museum of History, which showcases the history and culture of Osaka. Learn about the city's past and see artifacts from different periods.
• Next, head to the Namba district for some shopping and entertainment. Visit the Namba Parks shopping mall or catch a show at the Namba Grand Kagetsu theater.
• In the evening, take a stroll through the beautiful Osaka Castle Park and enjoy the peaceful surroundings.

I hope this itinerary helps you plan your trip to Osaka! Let me know if you have any other questions or need further assistance.