That's the difference between [e] and [ɛ] in IPA (in IPA, with "narrow" phonetic transcription, you enclose the sounds in brackets). In American English, "ace" is [eɪs] and "mess" is [mɛs]. But I don't think that's right; I'm pretty sure both the Japanese e and Spanish e sound exactly the same.

And if you pronounced [e] and [ɛ] to native speakers of either Spanish or Japanese, they most likely wouldn't be able to differentiate the two sounds consistently without having had training. I know that in Spanish, realization of e can be either vowel depending on the speaker and context; they might pronounce "tierra" as [tjɛra] and "mesa" as [mesa].