Fantasy
Illusion
noun, の adjective
An illusion that you imagine is your big fantasy (it's also an illusion). This makes sense, though, right? An illusion is an illusion, sure. But, when you imagine it, it becomes your fantasy!
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
フグはいくつになっても幻想の世界の住人なんだな。
No matter how old Fugu gets, he still lives in a world of illusion.
時々、コウイチが自分の息子だというあまい幻想をいだいています。
I sometimes cherish the sweet illusion that Koichi is my son.
私の兄は、自分が河豚の王だという馬鹿げた幻想を持ち続けている。
My older brother maintains the ridiculous fantasy that he is the king of the blowfish.