Collect all scattered across the maps. Complete Level 60 with full health remaining . If you'd like to dive deeper, let me know: Which specific level are you stuck on? Which character are you trying to max out? Do you need a list of all Hidden Memory Shard locations ?
For the completionists, here are final secrets: waifu crossing walkthrough
Receive gifts, updates, and letters from your waifus. Collect all scattered across the maps